This study was undertaken to evaluate the antitumor activities of Cordyceps militaris of silkworm pupa (CMP) and silkworm larva (CML), as compared with the effect of cordycepin, an active compound found in Cordyceps militaris. Antiproliferation effect of the test materials were evaluated in the sarcoma-180 cells using the MTT test. For the in vivo study, ICR mice were inoculated i.p. with 1.0 ${\times}$ 10$^{6}$ sarcoma-180 cells/mouse on Day 0, and were again i.p. injected with one of the following substances from Day 1 to Day 10 : saline (control group), 50 mg/kg (CMP50, CML50) ,100 ma/kg (CMP100, CML100), or 200 mg/kg (CMP200, CML200) of Cordyceps militaris water extracts, or 1 mg/kg (C1), 2 mg/kg (C2), or 4 mg/kg (C4) of cordycepin. Pretreatment of the sarcoma-180 cells with 100 mg/ml, 500 mg/ml, and 1000 mg/ml of CML (60.1$\pm$2.5％, 49.8$\pm$3.7％, and 45.4$\pm$0.1％ of the value for untreated control cells, respectively) or CMP (68.3$\pm$2.1％, 55.1$\pm$0.9％, and 51.4$\pm$3.5％ of the value for control cells, respectively) for 48 hrs significantly decreased the survival rate (proliferation) of tumor cells (p<0.05). Body weight of the control mice bearing ascites tumor and injected with saline was 1.4 times of the value for normal animals at day 18. Mice bearing ascites tumor and injected with cordycepin (1, 2, or 4 mg/kg) exhibited a significantly lighter body weight compared with the control mice, while animals injected with CMP or CML (50, 100, or 200 mg/kg) showed a significantly lighter body weight compared with the mice injected with cordycepin. Mice injected with CMP50, CMP100, or CMP200 mg/kg (or CML50, CML100, or CML200 mg/kg) showed a 133％ (or 90％), 80％ (or 62％), and 68％ (or 52％) longer mean survival time, and those treated with C1, C2, or C4 exhibited a 54％, 91％ and 80％ longer survival time compared to the value for control mice injected with saline. These results indicate that the hot-water extracts of Cordyceps militaris of both silkworm pupa and silkworm larva have an anti-proliferation effect of tumor cells as well as the life prolongation effect in mice bearing ascites tumor, which are superior to the activities of cordycepin.