What is the MLA font size?

Typically Times New Roman but.. Use a reasonably-sized font: either 10 characters per inch or a 12 point font. And choose a font that is easy to read rather one that is decorative: "Arial," "Lucida," "Modern," "Palermo" or "Times New Roman" are some good choices. Scripted fonts are hard to read even if they do make your paper "look nice"; it is the content of the paper that is most important, and making it easy for your readers to understand that content is always a good choice