diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index 360cadd0..f31683a3 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -180,6 +180,7 @@
     <Compile Include="Illusion\ArcPP.cs" />
     <Compile Include="Interheart\ImageBMP.cs" />
     <Compile Include="Interheart\ImageHMP.cs" />
+    <Compile Include="CatSystem\ArcZT.cs" />
     <Compile Include="JamCreation\ArcDAT.cs" />
     <Compile Include="JamCreation\ImageDPO.cs" />
     <Compile Include="AliceSoft\ArcAAR.cs" />
diff --git a/ArcFormats/CatSystem/ArcZT.cs b/ArcFormats/CatSystem/ArcZT.cs
new file mode 100644
index 00000000..d0a9e4b5
--- /dev/null
+++ b/ArcFormats/CatSystem/ArcZT.cs
@@ -0,0 +1,120 @@
+//! \file       ArcZT.cs
+//! \date       2021 May 25
+//! \brief      CatSystem2 pack file.
+//
+// Copyright (C) 2021 by morkt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using GameRes.Compression;
+
+namespace GameRes.Formats.CatSystem
+{
+    [Export(typeof(ArchiveFormat))]
+    public class ZtOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "ZT/PACK"; } }
+        public override string Description { get { return "CatSystem2 pack file"; } }
+        public override uint     Signature { get { return 0; } }
+        public override bool  IsHierarchic { get { return true; } }
+        public override bool      CanWrite { get { return false; } }
+
+        public ZtOpener ()
+        {
+            Extensions = new string[] { "zt" };
+        }
+
+        struct ZtSubdirectory
+		{
+            public string Name;
+            public long Offset;
+		}
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            if (file.MaxOffset < 0x11C)
+                return null;
+            if (0x110 > file.View.ReadUInt32 (8) || 1 < file.View.ReadUInt32 (0xC))
+                return null; // First entry is too small, or not a file or folder
+            var dir = new List<Entry> ();
+            var subdirs = new Queue<ZtSubdirectory> ();
+            const string sep = "\\";
+            string parent_name = "";
+            long offset = 0;
+            uint offset_next;
+            do
+            {
+                offset_next     = file.View.ReadUInt32 (offset);
+                uint entry_size = file.View.ReadUInt32 (offset+8);
+                if (0 != offset_next && 0xC + entry_size > offset_next)
+                    return null;
+                uint attributes = file.View.ReadUInt32 (offset+0xC);
+                string name     = file.View.ReadString (offset+0x10, 0x104);
+                if (1 < attributes || 0 == name.Length)
+                    return null;
+
+                if (0 == attributes)
+                {
+                    var entry = FormatCatalog.Instance.Create<PackedEntry> (parent_name + name);
+                    uint packed_size = file.View.ReadUInt32 (offset+0x114);
+                    if (0x110 + packed_size != entry_size)
+                        return null;
+                    entry.Offset = offset + 0x11C;
+                    entry.Size = packed_size;
+                    entry.UnpackedSize = file.View.ReadUInt32 (offset+0x118);
+                    entry.IsPacked = true;
+                    if (!entry.CheckPlacement (file.MaxOffset))
+                        return null;
+                    dir.Add (entry);
+                }
+                else if (0 != file.View.ReadUInt32 (offset+4))
+                {
+                    subdirs.Enqueue (new ZtSubdirectory { Name = parent_name + name + sep, Offset = offset });
+                }
+
+                if (0 == offset_next && 0 != subdirs.Count)
+                {   // No more entries in current directory, go to next subdirectory
+                    var subdir = subdirs.Dequeue ();
+                    parent_name = subdir.Name;
+                    offset      = subdir.Offset;
+                    offset_next = file.View.ReadUInt32 (offset+4); // offset_child
+                    if (0xC + file.View.ReadUInt32 (offset+8) > offset_next)
+                        return null;
+                }
+                offset += offset_next;
+            }
+            while (0 != offset_next);
+
+            return new ArcFile (file, this, dir);
+        }
+
+        public override Stream OpenEntry (ArcFile arc, Entry entry)
+        {
+            var pentry = (PackedEntry)entry;
+            if (0 == pentry.UnpackedSize)
+                return Stream.Null;
+            var input = arc.File.CreateStream (entry.Offset, entry.Size);
+            return new ZLibStream (input, CompressionMode.Decompress);
+        }
+    }
+}