In this study, we investigated the antioxidant activity and anticancer effect of Coprinus comatus (C. comatus) extracts. Free radical scavenging capacity of the C. comatus extracts was evaluated in vitro by the DPPH assay. C. comatus exhibited the strong DPPH radical scavenging activity. In vitro tests were also performed to examine the anticancer activity of C. comatus against 293 human normal epithelial kidney cells and various human cancer cell lines including AGS, Hela and HCT-15. C. comatus extracts showed the potent cancer cell-selective growth inhibitory activity against AGS, Hela, and HCT-15 cells, but slightly inhibited 293 normal cell growth. We examined several biological activities such as antitumor effects of C. comatus extracts in vivo. Solid tumors were induced by Sarcoma-180 inoculation in the left groin of BALB/c mice and then C. comatus extracts were oral administered. After 5 weeks, all mice were sacrificed and their tumor weights were measured. C. comatus extracts exhibited the most effective antitumor activity, and the tumor growth rate was inhibited by 55% in comparison with control group. Taken together, these results indicate that C. comatus extracts showed high antioxidant activity and possessed powerful antitumor activity.