The present invention relates to a process for producing 3-methylcyclopentadecane-1,5-dione of formula (I), which comprises the oxidation of 14-methyl-bicyclo[10.3.0]pentadecen[1 (12)] of formula (II) with an oxidizing agent, where the oxidation is performed by using a mixture of formic acid with H2O2 as sole oxidizing agent in the presence of water and where the amount of H2O2 is at least 1.1 mol H2O2 per mol of the compound of formula (II).