To reproduce: Try setting the value in the CellForamting event. Workaround: class MySpreadExportRenderer : SpreadExportRenderer { public override void SetCellSelectionValue(DataType dataType, object value) { base.SetCellSelectionValue(dataType, value); if (dataType == DataType.Number) { CellRange range = ((CellSelection)this.GetCellSelection()).CellRanges.ElementAtOrDefault(0); double d; if (double.TryParse(Convert.ToString(value), out d)) { var cell = ((Worksheet)this.GetWorksheet()).Cells[range.FromIndex.RowIndex, range.FromIndex.ColumnIndex]; cell.SetFormat(new CellValueFormat("#,##0.00")); cell.SetValue(d); } } } }