S‐Alkylthiocarboxylic acids and their potassium salts were prepared by photoaddition of α‐olefins (C10, C12, and C14) with mercapto carboxylic acids such as thiomalic acid, thiopropionic acid, and thioglycolic acid. The physicochemical solution properties and thermal stabilities for three series of thiosurfactants were evaluated. S‐Alkylthiocarboxylic acids that contain bridged S‐bonds provide excellent thermally stable surfactants, and their alkaline salts exhibit good surface activity.