A process for producing muscone by methyl addition to the 1,4-conjugation of 2-cyclopentadecenone. By the process, muscone is produced in high yield not under reaction condition including an extremely low temperature and a low concentration but under practical condition. The process comprises subjecting 2-cyclopentadecenone to a 1,4-conjugation addition reaction with an organometallic methylation reagent in the presence of a copper or nickel catalyst and an enol anion scavenger to obtain a 3-methyl-1-cyclopentadecene derivative represented by General Formula (II) and then solvolyzing the enol moiety of the 3-methyl-1-cyclopentadecene derivative to obtain muscone.