This study was devised to observe the antitumor activity of mugwort (Artemisia princeps Pampan.) against ICR mice inoculated with sarcoma-180 cells. The antitumor compounds were partially purified from petroleum ether extract of mugwort by silicic acid column chromatography. The active fraction used in in vivo test was obtained under the elution with acetone in silicic acid column chromatography. When the acetone fraction was intraperitoneally injected to the mice which had been subcutaneously inoculated on the left groin with sarcoma-180, the growth rate of tumor (sarcoma-180 mass) was inhibited by 30%. In case the acetone fraction was injected to the mice which had been inoculated intraperitoneally with sarcoma-180, the average life span was prolonged by 20%. After the injection of the active fraction, the spleen index and ${gamma}-globulin$ ratio (%) were increased significantly (p<0.05). The administration of acetone fraction did not cause any abnormality in the body and the homeostasis of mice. Those observations suggest that the acetone fraction of mugwort extract has an antitumor effect in vivo.