Acetylsalicylic acid (aspirin) inhibited ethylene production of apple (Malus domestica Borkh. cv. Granny Smith) fruit discs in a concentration and time-dependent fashion. Activity of 1-aminocyclopropane-1-carboxylic acid (ACQ oxidase was inhibited both in vivo and in vitro by acetylsalicylic acid, both V max and K m decreased as acetylsalicylic acid concentration increased. The apparent Ki was 0.12 mmol·L −1 . We conclude acetylsalicylic acid inhibits ethylene production by inhibiting ACC oxidase activity. For unknown reasons, acetylsalicylic acid also inhibited fruit respiration.