In PowerPoint, the default font for any text is Arial, 18 points. If you need another font and don’t want to go through the hassle of having to select text each time and change the default font in PowerPoint, do the following:
In PowerPoint 2003:
Go to Format>Font> Choose the attributes and click on OK to save changes. In PowerPoint 2007:
Go to Home>Shapes>Basic Shapes>Text Box. Draw a text box on the slide, choose font attributes and right click on the border of the text box and choose Set as Default Text Box from the menu. To ensure that this is the default for the presentation, do this before you start working on your presentation.