Shocking to me that this can still be broken. It compiles with the code. using System.IO.Compression; FileStream fileStream = new FileStream(filename, FileMode.Create, FileAccess.Write); GZipStream compressionStream = new GZipStream(fileStream, CompressionMode.Compress); StreamWriter writer = new StreamWriter(compressionStream); But when used it gives this error. DllNotFoundException: MonoPosixHelper System.IO.Compression.DeflateStream..ctor (System.IO.Stream compressedStream, CompressionMode mode, Boolean leaveOpen, Boolean gzip) I'm not the one on crack here. Unity obviously has zip , check their folder zlib1.dll It's been broken since unity 3 and apparently they never plan on fixing it.