Fermentation processes using cordycepinproducing fungi other than O. sinensis may be an alternative way to produce cordycepin, which is a nucleoside analogue compound possessing many pharmacological functions. In order to screen cordycepinproducing fungi from traditional Chinese medicine Ophiocordyceps sinensis, we isolated a total of 42 fungal strains from the fruiting bodies of O. sinensis. In the present study, a cordycepinproducing fungal strain OS17 was isolated from O. sinensis. The strain produced cordycepin when grown in potato dextrose broth (PDB) medium, and the amount of cordycepin produced by this fungus was quantified to be 40.16 mg/L by HPLC. The fungal cordycepin which was analyzed by HPLC was shown to be identical to authentic cordycepin. The strain OS17 was identified as Bionectria ochroleuca based on its morphology and ITS sequence analysis. To the best of our knowledge, this is the first report concerning the isolation and identification of cordycepinproducing Bionectria spp. from its host, which showed that endophytic fungi have the potential to produce many bioactive compounds.