十五酸（Pentadecanoic acid），分子式CH₃(CH₂)₁₃COOH。这种脂肪酸可以在奶牛的乳汁中微量找到。 牛奶也是十五酸的主要来源

不饱和脂肪酸

Pentadecanoic acid is a saturated fatty acid. Its molecular formula is CH₃(CH₂)₁₃COOH. It is rare in nature, being found at the level of 1.2% in the milk fat from cows. The butterfat in cows milk is its major dietary source and it is used as a marker for butterfat consumption. Pentadecanoic acid also occurs in hydrogenated mutton fat.