As said, the equation is not being converted: It is always a textbox (also in the original file). The problem is that Excel 2010 added some extra formatting to allow the textbox to show equations, and it is saving both versions in the file. FlexCel is reading the oldest version available (2007) to ensure all Excel users can read the file it creates. We should modify it to read both versions and save both too, but this isn't technically simple. As said, I'll study what can be done and let you know. Right now, FlexCel is behaving in this case as if an user of Excel 2007 opened and saved the file.