不要与组织胺(histamine, C₅H₉N₃)混淆。

组氨酸（英语：Histidine，, C₆H₉N₃O₂）简写为His或H，α氨基酸结合咪唑官能团。是存在于蛋白质之中最普遍的23种氨基酸之一。初以为只针对婴幼儿是必需的，较长期的研究表明，它也是成年人必不可少的必需氨基酸。等电点为7.59，是碱性氨基酸，生理条件下带正电荷。他的合成密码子为 CAU 及 CAC。组氨酸在1896年由德国医师艾布瑞契·科塞尔(Albrecht Kossel)首次分离出来。

Histidine (abbreviated as His or H; encoded by the codons CAU and CAC) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH₃ form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO form under biological conditions), and a side chain imidazole, classifying it as a positively charged (at physiological pH). Initially thought essential only for infants, longer-term studies have shown it is essential for adults also.