To find antitumor components in the hot water extract of the cultured mycelia of Ganoderma lucidum, protein-bound polysaccharides were purified and fractionated (Fr. I-V) by DEAE-cellulose ion exchange column chromatography and Sepbarose CL-4B gel filtration. When a dose of 20 mg/kg/day of each was, i.p., injected into ICR mice, the inhibition ratios against the solid form of sarcoma 180 were $64.2{sim}75.8%$. The antitumor component was examined for immunological activity. It increased the amount of superoxide anion released by induced macrophages in peritoneal cavity to 1.8 times and the count of hemolytic plaque-forming cells (PFC) was increased to 4.4 times as compared with those of the control group. It contained 68.6% polysaccharide which consisted of mannose, glucose, galactose, fucose and xylose and 5.1% protein consisting of 17 amino acids. The contents of hexosamine were 0.78%. The molecular weight of Fr. V that showed the highest antitumor activity was $5.8{ imes}10^4$ dalton by Sepharose CL-4B gel filtration. It was named lucidan.