Chuling, sclerotia of Polyporus umbellatus FRIES, has long been used for urological disorders in traditional medicine. In this study, we demonstrated that Chuling in vitro protects red blood cells from 2,2-azo-bis(2-amidinopropane)dihydrochloride (AAPH)-induced hemolysis. The inhibitory effect was dose-dependent at concentrations of 50 to 1000 microg/ml. Moreover, tests were carried out to identify the main ingredient of Chuling with scavenging effect on free radicals. Triterpene carboxylic acids isolated from the methanol extract of Chuling, namely, polyporusterone A and polyporusterone B, were found to have inhibitory activities against AAPH-induced lysis of red blood cells. The anti-hemolytic effect was significantly stronger in polyporusterone B compared with polyporusterone A. Furthermore, the ingestion of 150 mg of Chuling was associated with a significant increase in free-radical scavenging effect of plasma in rats.