Ƙungiyar carboxyl ƙungiya ce mai aiki da ta ƙunshi atom ɗin carbon wanda aka haɗa biyu zuwa atom ɗin oxygen da haɗin kai ɗaya zuwa ƙungiyar hydroxyl (-OH). Yawancin lokaci ana rubuta shi azaman -COOH ko -CO2H. Ana samunsa a cikin mahadi masu yawa, irin su amino acid, fatty acids, da acid carboxylic, kuma yana da alhakin halayen acidic. Ƙungiyar carboxyl kuma za ta iya shiga cikin halayen sinadarai kamar esterification da amidation.