PURPOSE: To obtain beta-isophorone by using heterogeneous catalysts, such as Ni oxide and Al oxide, in a gaseous phase, thereby cost effectively and advantageously subjecting alpha-isophorone to isomerization at a high yield.

CONSTITUTION: The alpha-isophorone is converted to the beta-isophorone in the gaseous phase by using the catalysts consisting of the Ni oxide calcined at ≥1000°C on the carrier of the oxide of Mg, Al, Si and Ni or mixed oxide, more particularly γ-aluminum oxide as the heterogeneous catalysts. The specific surface area of the catalysts is 1 to 50 m2/g and the catalysts having the least possible quantity of micropores and small apertures are preferable. The alpha- isophorone is preferably used at 1 to 10 kg per 1 liter catalysts and per hour. The reaction is adequatly executed at about 300 to 450°C for a contact time of 0.1 to 10 seconds under a pressure of 1 to 200 kPa.