To provide a method for continuously producing β-isophorone by isomerization of α-isophorone in the presence of a homogeneous catalyst which can be obtained by the trimerization of acetone in an alkali medium.

This method comprises the following processes: (a) continuously feeding α-isophorone and an alkali hydroxide solution into a reaction zone; (b) heating the reaction mixture at least up to 150°C; (c) continuously and simultaneously conducting (1) removal of a fraction containing 30-90 wt.% β- isophorone by distillation at 150-216°C under a pressure ranging from 350 millibars to atmospheric pressure and (2) an operation extracting heavy reaction products to lower its content in the reaction mixture down to ≤7 wt.%; (d) continuously rectifying the above fraction under reduced pressure at 100-150°C keeping pace with the distillation in the step (1) in the process (c) so as to obtain purified β-isophorone having ≥99% of a content ratio of β-isophorone to α-isophorone; and (e) continuously returning remainder in the rectifier to the reaction zone.