丙酸(propanoic acid)，又称初油酸，是三个碳的羧酸和短链饱和脂肪酸，化学式为CH₃CH₂COOH。纯的丙酸是无色、腐蚀性的液体，带有刺激性气味。

工业上丙酸是通过四羰基镍催化剂存在下，乙烯的加氢羧化反应制得的：

RCH=CH₂ + H₂O + CO → CH₃CH₂CO₂H

它也可以通过丙醛的氧气氧化得到。在钴或锰离子存在下，该反应在40-50°C即可发生：

CH₃CH₂CHO + ½ O₂ → CH₃CH₂COOH

以前乙酸的生产会产生大量的丙酸副产品。

Propionic acid (from the Greek words protos, meaning "first", and pion, meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula CH₃CH₂COOH. It is a clear liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH₃CH₂COO as well as the salts and esters of propionic acid are known as propionates (or propanoates).