PURPOSE: To obtain a cyclic ketone in good yield with easy post-treatment and easy recovery of solvent and catalyst by making an epoxide to be subjected to rearrangement reaction to isomerize in a polar solvent in the presence of an alkaline halide salt at particular temperature.

CONSTITUTION: This cyclic ketone comprising 7-20 ring carbon atoms particularly comprising 5-17 carbon atoms and containing up to 5 carbon-multiplebonds and side chain of formula I (R is H, CH3, C2H5, C2H3, C3H7, C5H9, or the like; (a) and (b) are each 7-20 of ring carbon atoms) such as cyclododecanone, etc., being useful as expensive perfume, etc., formula II, formula III (c=a or c) formula IV (d=a, b or c) or formula V (e=a, b, c or d), etc., is obtained by making an epoxide such as epoxicyclododecane, etc., being accessible industrially from cycloolefin to be subjected to rearrangement reaction to isomerize in a polar solvent such as N,N'-dimethylethyleneurea, etc., in the presence of an alkaline (earth) halide catalyst such as LiCl, etc., at a temp. of 120 to 250°C.