Unfortunately, Microsoft Office Visio does not support fitting a line of text to a curve. You can, however, create text that follows a curved path using WordArt in Office Word or Office PowerPoint. You can then copy and paste the WordArt into Visio.
Note: For information about how to create WordArt in Microsoft Office Word 2007 or Microsoft Office PowerPoint Viewer 2007, see Add, change, or delete WordArt.
To copy and paste WordArt into your Visio diagram:
Select the WordArt, and press Ctrl+C.
In the Visio diagram, press Ctrl+V.