The present invention relates to a method for producing a 3-methylcycloalkenone compound and a method for producing muscone. In the presence of a zirconium oxide catalyst, a diketone represented by the following general formula (1): wherein in formula (1), n represents 8, 9, 10, 11 or 12, is subjected to a vapor-phase intramolecular condensation reaction, whereby a 3-methylcycloalkenone compound can be produced with high reaction efficiency. When a 3-methylcyclopentadecenone compound produced by this method is hydrogenated in a known manner, muscone can be produced efficiently.