diff --git a/OpenTween/Api/DataModel/MastodonAccount.cs b/OpenTween/Api/DataModel/MastodonAccount.cs
new file mode 100644
index 000000000..3dfb2d88b
--- /dev/null
+++ b/OpenTween/Api/DataModel/MastodonAccount.cs
@@ -0,0 +1,73 @@
+// OpenTween - Client of Twitter
+// Copyright (c) 2017 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
+// All rights reserved.
+//
+// This file is part of OpenTween.
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+// for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
+// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+// Boston, MA 02110-1301, USA.
+
+using System.Runtime.Serialization;
+
+namespace OpenTween.Api.DataModel
+{
+    public class MastodonAccount
+    {
+        [DataMember(Name = "id")]
+        public long Id { get; set; }
+
+        [DataMember(Name = "username")]
+        public string Username { get; set; }
+
+        [DataMember(Name = "acct")]
+        public string Acct { get; set; }
+
+        [DataMember(Name = "display_name")]
+        public string DisplayName { get; set; }
+
+        [DataMember(Name = "locked")]
+        public bool Locked { get; set; }
+
+        [DataMember(Name = "created_at")]
+        public string CreatedAt { get; set; }
+
+        [DataMember(Name = "followers_count")]
+        public int FollowersCount { get; set; }
+
+        [DataMember(Name = "following_count")]
+        public int FollowingCount { get; set; }
+
+        [DataMember(Name = "statuses_count")]
+        public int StatusesCount { get; set; }
+
+        [DataMember(Name = "note")]
+        public string Note { get; set; }
+
+        [DataMember(Name = "url")]
+        public string Url { get; set; }
+
+        [DataMember(Name = "avatar")]
+        public string Avatar { get; set; }
+
+        [DataMember(Name = "avatar_static")]
+        public string AvatarStatic { get; set; }
+
+        [DataMember(Name = "header")]
+        public string Header { get; set; }
+
+        [DataMember(Name = "header_static")]
+        public string HeaderStatic { get; set; }
+    }
+}
diff --git a/OpenTween/Api/DataModel/MastodonApplication.cs b/OpenTween/Api/DataModel/MastodonApplication.cs
new file mode 100644
index 000000000..2898f7587
--- /dev/null
+++ b/OpenTween/Api/DataModel/MastodonApplication.cs
@@ -0,0 +1,34 @@
+// OpenTween - Client of Twitter
+// Copyright (c) 2017 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
+// All rights reserved.
+//
+// This file is part of OpenTween.
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+// for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
+// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+// Boston, MA 02110-1301, USA.
+
+using System.Runtime.Serialization;
+
+namespace OpenTween.Api.DataModel
+{
+    public class MastodonApplication
+    {
+        [DataMember(Name = "name")]
+        public string Name { get; set; }
+
+        [DataMember(Name = "website")] // Nullable
+        public string Website { get; set; }
+    }
+}
diff --git a/OpenTween/Api/DataModel/MastodonAttachment.cs b/OpenTween/Api/DataModel/MastodonAttachment.cs
new file mode 100644
index 000000000..32bba1c18
--- /dev/null
+++ b/OpenTween/Api/DataModel/MastodonAttachment.cs
@@ -0,0 +1,46 @@
+// OpenTween - Client of Twitter
+// Copyright (c) 2017 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
+// All rights reserved.
+//
+// This file is part of OpenTween.
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+// for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
+// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+// Boston, MA 02110-1301, USA.
+
+using System.Runtime.Serialization;
+
+namespace OpenTween.Api.DataModel
+{
+    public class MastodonAttachment
+    {
+        [DataMember(Name = "id")]
+        public long Id { get; set; }
+
+        [DataMember(Name = "type")]
+        public string Type { get; set; }
+
+        [DataMember(Name = "url")]
+        public string Url { get; set; }
+
+        [DataMember(Name = "remote_url")]
+        public string RemoteUrl { get; set; }
+
+        [DataMember(Name = "preview_url")]
+        public string PreviewUrl { get; set; }
+
+        [DataMember(Name = "text_url")]
+        public string TextUrl { get; set; }
+    }
+}
diff --git a/OpenTween/Api/DataModel/MastodonMention.cs b/OpenTween/Api/DataModel/MastodonMention.cs
new file mode 100644
index 000000000..3bc1af9dd
--- /dev/null
+++ b/OpenTween/Api/DataModel/MastodonMention.cs
@@ -0,0 +1,40 @@
+// OpenTween - Client of Twitter
+// Copyright (c) 2017 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
+// All rights reserved.
+//
+// This file is part of OpenTween.
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+// for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
+// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+// Boston, MA 02110-1301, USA.
+
+using System.Runtime.Serialization;
+
+namespace OpenTween.Api.DataModel
+{
+    public class MastodonMention
+    {
+        [DataMember(Name = "url")]
+        public string Url { get; set; }
+
+        [DataMember(Name = "username")]
+        public string Username { get; set; }
+
+        [DataMember(Name = "acct")]
+        public string Acct { get; set; }
+
+        [DataMember(Name = "id")]
+        public long Id { get; set; }
+    }
+}
diff --git a/OpenTween/Api/DataModel/MastodonStatus.cs b/OpenTween/Api/DataModel/MastodonStatus.cs
new file mode 100644
index 000000000..0951ebe87
--- /dev/null
+++ b/OpenTween/Api/DataModel/MastodonStatus.cs
@@ -0,0 +1,88 @@
+// OpenTween - Client of Twitter
+// Copyright (c) 2017 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
+// All rights reserved.
+//
+// This file is part of OpenTween.
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+// for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
+// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+// Boston, MA 02110-1301, USA.
+
+using System.Runtime.Serialization;
+
+namespace OpenTween.Api.DataModel
+{
+    public class MastodonStatus
+    {
+        [DataMember(Name = "id")]
+        public long Id { get; set; }
+
+        [DataMember(Name = "uri")]
+        public string Uri { get; set; }
+
+        [DataMember(Name = "url")]
+        public string Url { get; set; }
+
+        [DataMember(Name = "account")]
+        public MastodonAccount Account { get; set; }
+
+        [DataMember(Name = "in_reply_to_id")]
+        public long? InReplyToId { get; set; }
+
+        [DataMember(Name = "in_reply_to_account_id")]
+        public long? InReplyToAccountId { get; set; }
+
+        [DataMember(Name = "reblog")]
+        public MastodonStatus Reblog { get; set; }
+
+        [DataMember(Name = "content")]
+        public string Content { get; set; }
+
+        [DataMember(Name = "created_at")]
+        public string CreatedAt { get; set; }
+
+        [DataMember(Name = "reblogs_count")]
+        public int ReblogsCount { get; set; }
+
+        [DataMember(Name = "favourites_count")]
+        public int FavouritesCount { get; set; }
+
+        [DataMember(Name = "reblogged")]
+        public bool Reblogged { get; set; }
+
+        [DataMember(Name = "favourited")]
+        public bool Favourited { get; set; }
+
+        [DataMember(Name = "sensitive")]
+        public bool? Sensitive { get; set; }
+
+        [DataMember(Name = "spoiler_text")]
+        public string SpoilerText { get; set; }
+
+        [DataMember(Name = "visibility")]
+        public string Visibility { get; set; }
+
+        [DataMember(Name = "media_attachments")]
+        public MastodonAttachment[] MediaAttachments { get; set; }
+
+        [DataMember(Name = "mentions")]
+        public MastodonMention[] Mentions { get; set; }
+
+        [DataMember(Name = "tags")]
+        public MastodonTag[] Tags { get; set; }
+
+        [DataMember(Name = "application")]
+        public MastodonApplication Application { get; set; }
+    }
+}
diff --git a/OpenTween/Api/DataModel/MastodonTag.cs b/OpenTween/Api/DataModel/MastodonTag.cs
new file mode 100644
index 000000000..77258710c
--- /dev/null
+++ b/OpenTween/Api/DataModel/MastodonTag.cs
@@ -0,0 +1,34 @@
+// OpenTween - Client of Twitter
+// Copyright (c) 2017 kim_upsilon (@kim_upsilon) <https://upsilo.net/~upsilon/>
+// All rights reserved.
+//
+// This file is part of OpenTween.
+//
+// This program is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+// for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>, or write to
+// the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+// Boston, MA 02110-1301, USA.
+
+using System.Runtime.Serialization;
+
+namespace OpenTween.Api.DataModel
+{
+    public class MastodonTag
+    {
+        [DataMember(Name = "name")]
+        public string Name { get; set; }
+
+        [DataMember(Name = "url")]
+        public string Url { get; set; }
+    }
+}
diff --git a/OpenTween/OpenTween.csproj b/OpenTween/OpenTween.csproj
index 2182b4f78..e1a633909 100644
--- a/OpenTween/OpenTween.csproj
+++ b/OpenTween/OpenTween.csproj
@@ -71,6 +71,12 @@
     <Compile Include="Api\ApiLimit.cs" />
     <Compile Include="Api\BitlyApi.cs" />
     <Compile Include="Api\DataModel\GeoJson.cs" />
+    <Compile Include="Api\DataModel\MastodonAccount.cs" />
+    <Compile Include="Api\DataModel\MastodonApplication.cs" />
+    <Compile Include="Api\DataModel\MastodonAttachment.cs" />
+    <Compile Include="Api\DataModel\MastodonMention.cs" />
+    <Compile Include="Api\DataModel\MastodonStatus.cs" />
+    <Compile Include="Api\DataModel\MastodonTag.cs" />
     <Compile Include="Api\DataModel\TwitterConfiguration.cs" />
     <Compile Include="Api\DataModel\TwitterEntity.cs" />
     <Compile Include="Api\DataModel\TwitterError.cs" />