This study was carried out to investigate chemical ingredient of Cryptoporus vovatus . Methanol extract of Cryptoporus vovatus was analyzed by column chromatography, thin layer chromatography, HPLC, mass spectrophotometer. CVM33100Me21 was isolated by prep-HPLC from methylene chloride fraction. From the physico-chemical data, including NMR, MS, the chemical structure of the compound was determined to be an ergosterol peroxide. (Fig. 1)