Xanthine ( or , from Ancient Greek ξανθός xanthós "yellow" due to its yellowish-white appearance; archaically xanthic acid; systematic name 3,7-dihydropurine-2,6-dione) is a purine base found in most human body tissues and fluids, as well as in other organisms. Several stimulants are derived from xanthine, including caffeine, theophylline, and theobromine.

Xanthine is a product on the pathway of purine degradation.

• It is created from guanine by guanine deaminase.
• It is created from hypoxanthine by xanthine oxidoreductase.
• It is also created from xanthosine by purine nucleoside phosphorylase.

Xanthine is subsequently converted to uric acid by the action of the xanthine oxidase enzyme.