Cordyceps sinensis is a parasitic fungus that has been used as a Chinese medicine for a long time. In the present study, inhibitory effects of crude methanolic extracts of C. sinensis fruiting bodies on various tumor cell lines were demonstrated. The crude methanolic extracts were fractionated into 15 fractions by silica gel column chromatography. Two of the 15 fractions (CS-36-39 and CS-48-51) significantly inhibited the growth of K562, Vero, Wish, Calu-1, and Raji tumor cell lines. The inhibitory activities were not due to the polysaccharides, which have been removed in the extracting process. The polarities of these two fractions indicated that they were different from that of cordycepin. Therefore, it is suggested that tumor cell growth inhibitors, other than cordycepin and polysaccharides, are contained in C. sinensis.