Essential oils of the musk from wild muskrat (Ondatra zibethicus) were analyzed by gas chromatography/mass spectrometry. Fifty-six chemical components were separated, and 14 volatile compounds (78% of composition of total essential oil) of macrocyclic musk, mainly cyclopentadecanone, 12-hydroxy-14-methyl-oxa-cyclotetradec-6-en-2-one, cycloheptadecanone and 9-cycloheptadecen-1-one, were identified by the comparison of Wiley/NBS Library from the results of GC-MS. However, l-muscone, a compound reported by earlier workers in the musk from muskrat, was not detected using the spike test in this study. Interestingly, cyclohexadecanone, which has the same molecular weight (Mw 238) as l-muscone, was identified. In addition, it is considered that because of possessing much higher amounts of macrocyclic components compared to the original musk, muskrat has higher economic values in perfume and pharmaceutical industries.