乙酸，也叫醋酸、冰醋酸，化学式CH₃COOH，是一种有机一元酸和短链饱和脂肪酸，为食醋内酸味及刺激性气味的来源。纯的无水乙酸（冰醋酸）是无色的吸湿性固体，凝固点为16.7℃（62℉），凝固后为无色晶体。尽管根据乙酸在水溶液中的解离能力它是一种弱酸，但是乙酸是具有腐蚀性的，其蒸汽对眼和鼻有刺激性作用。

乙酸是一种简单的羧酸，由一个甲基一个羧基组成，是一种重要的化学试剂。在化学工业中，它被用来制造聚对苯二甲酸乙二酯，后者即饮料瓶的主要部分。乙酸也被用来制造电影胶片所需要的醋酸纤维素和木材用胶粘剂中的聚乙酸乙烯酯，以及很多合成纤维和织物。家庭中，乙酸稀溶液常被用作除垢剂。食品工业方面，在食品添加剂列表E260中，乙酸是规定的一种酸度调节剂。

Acetic acid /əˈsiːtᵻk/, systematically named ethanoic acid /ˌɛθəˈnoʊᵻk/, is a colourless liquid organic compound with the chemical formula CH₃COOH (also written as CH₃CO₂H or C₂H₄O₂). When undiluted, it is sometimes called glacial acetic acid. Vinegar is roughly 3–9% acetic acid by volume, making acetic acid the main component of vinegar apart from water. Acetic acid has a distinctive sour taste and pungent smell. In addition to household vinegar, it is mainly produced as a precursor to polyvinyl acetate and cellulose acetate. Although it is classified as a weak acid, concentrated acetic acid is corrosive and can attack the skin.