The reactions of n-Bu2Zn and n-Bu3Al with α,β-unsaturated ketones were studied. The elementary reactions were found to be conjugate addition and hydrogen abstraction reactions. One n-butyl group of metal alkyl was consumed in the conjugate addition, in contrast to the hydrogen abstraction reaction, all n-butyl groups being consumed in the latter elementary reaction. Conjugate addition rate constants were calculated regarding the conjugate addition as a second-order reaction with metal alkyl. On the basis of the kinetic data, infrared spectra of the reaction system, and the relative reactivity of the homologous vinyl ketones (α-methyl-substituted > unsubstituted > β-methyl-substituted), a four-centred mechanism was presented for the conjugate addition reaction of the metal alkyl with α, β-unsaturated ketone.