//...POST working fine private void ClientCall() { try { var client = new HttpClient(); var fileInfo = new FileInfo("D:\\index.html"); var fileContent = new StreamContent(fileInfo.OpenRead()); fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") { Name = "\"file\"", FileName = "\"" + fileInfo.Name + "\"" }; fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse(MimeMapping.GetMimeMapping(fileInfo.Name)); // This is the postdata var postData = new List <KeyValuePair <string, string> >(); postData.Add(new KeyValuePair <string, string>("file", fileContent.ToString())); postData.Add(new KeyValuePair <string, string>("style", "Basic")); postData.Add(new KeyValuePair <string, string>("Client ", "Springer")); postData.Add(new KeyValuePair <string, string>("style", "Basic")); postData.Add(new KeyValuePair <string, string>("Language ", "En")); postData.Add(new KeyValuePair <string, string>("Format", "color")); // HttpContent content = new FormUrlEncodedContent(postData); MultipartFormDataContent form = new MultipartFormDataContent(); form.Add(new StringContent("Basic"), "style"); form.Add(new StringContent("Springer"), "Client"); form.Add(new StringContent("Basic"), "style"); form.Add(new StringContent("En"), "Language"); form.Add(new StringContent("color"), "Format"); client.PostAsync("http://192.168.84.140/cgi-enabled/Reflexica.cgi", form).ContinueWith( (postTask) => { var res = postTask.Result.Content.ReadAsStringAsync(); postTask.Result.EnsureSuccessStatusCode(); }); } catch (Exception ex) { throw new Exception(ex.Message); } }