In this study, the antitumor activities were investigated using $eta$-lmmunan, a proteoglycan obtained from cultured mycelia of the IY009 strain of Ganoderma lucidum belonging to basidiomycetes. The result showed the significant effect of cytotoxicity test against murine sarcoma 180 and murine lymphocytic leukemia L1210 using immunized macrophage cultures by $eta$-lmmunan. When intraperitoneally injected at 40 mg/kg/day daily for 10 days, $eta$-lmmunan inhibited the growth of sarcoma 180 solid tumor in ICR mice by 88.8% (p<0.05). It was also observed that $eta$-lmmunan increased life span by 85.2% (p<0.01) after treatment of 100 mg/kg/day in BDF1 mice bearing lymphocytic leukemia L1210. And combination therapy with cisplatin (dosage: 4 mg/kg) increased life span by 140.4% (p<0.05) after treatment of 100 mg/kg/day daily in BDF1 mice bearing lymphocytic leukemia L1210.