public void WorksheetPasteDate() { MemoryStream stream = SpreadsheetReader.Create(); SpreadsheetDocument doc = SpreadsheetDocument.Open(stream, true); WorksheetPart worksheetPart = SpreadsheetReader.GetWorksheetPartByName(doc, "Sheet1"); WorksheetWriter writer = new WorksheetWriter(doc, worksheetPart); Cell cell = writer.PasteDate("D3", new DateTime(2009, 12, 20, 15, 23, 05)); //Save to the memory stream, and then to a file SpreadsheetWriter.Save(doc); SpreadsheetWriter.StreamToFile(string.Format("{0}\\date.xlsx", GetOutputFolder()), stream); }