Hi,
Formatting the DateTime to specific string will not display as expected in the excel file, because the Excel cell format will override it.
you need to format the cell not the date time.
Microsoft.Office.Interop.Excel.Range range = worksheet.Cells[1,1] as Range;
range.NumberFormat = "dd/MMM/yyyy";
range.Value2 = DateTime.Now;
Regards
Jegan