What is a _XLS file? An _XLS file is a Microsoft Excel spreadsheet that has had its extension changed from .XLS to ._xls . A user or program may have changed the file's extension on purpose or by accident. _XLS files can be opened in Microsoft Excel and other spreadsheet programs after you rename them to use the .xls extension.

More Information _XLS files are almost always renamed XLS files. Most commonly, email programs such as Windows Live Mail mistakenly produce _XLS files. This happens when a user attaches a spreadsheet whose filename ends in . to an email. For example, if you attach a spreadsheet named spreadsheet..xls to an email, Windows Live Mail will rename that file to spreadsheet._xls . This issue also occurs when users attach .DOC , .DOCX , and .XLSX files to emails. While XLS, and thus _XLS, files are typically created by Microsoft Excel, they can also be created using other spreadsheet programs, such as OpenOffice Calc or Apple Numbers. After renaming your _XLS file to use the .xls extension, you should be able to open the file in any of those programs.