The anti-tumor effect of Cetraria laevigata polysaccharides has been investigated in mice using sarcoma 180; Ehrlich ascitic tumor, cervical carcinoma u-14 and leukemia L7217. The results show that Cetraria laevigata polysaccharides may inhibit the growth of sarcoma 180, Ehrlich ascitic tumor and cervical carcinoma u-14 in mice at a dose of 200mg/kg ip (1/5 LD50). However, the survival time of leukemia L7217 wasn't prolonged. The reticuloendothelial system phagocytic function in mice was increased at ip doses of 50 mg/kg and 100 mg/kg (1/10 and 1/20 LD50).