Polygonum hypoleucum Ohwi (P. hypoleucum Ohwi) has been used as a Chinese medicine for a long time. In the present study, four anthraquinones, emodin, emodin 1-O-beta-D-glucoside (49A), physcion (62A), and physcion 1-O-beta-D-glucoside (50A) were identified from P. hypoleucum Ohwi and their inhibitory effects on various tumor cells proliferation were investigated. On a percentage basis, emodin had the highest suppressing activity on the various tumor cells proliferation. At 10 microg/ml, the percentage inhibition on K562 cells proliferation for emodin, 49A, 62A, and 50A were 97+/-3.4%, 18+7.3%, 24+/-3.6%, and 31+/-8.9%, respectively. However, inhibitory activities of 10 microg/ml of emodin, 49A, 62A, or 50A on Raji cells proliferation were 98+/-5.0%, 25+/-5.0%, 22+/-3.2%, and 28+/-4.3%, respectively. It was also found that the both C1 and C3 positions of emodin were important for antitumor action. The IC50s of emodin, 49A, 62A, and 50A on various tumor cells were also calculated. The IC50 of emodin on K562 cells was significantly lower than on Raji, HeLa, Calu-1, Wish, and Vero cells (1.5+/-0.2 vs. 2.8+/-0.4 microg/ml, P < 0.01 ;1.5+/-0.2 vs. 8.4+/-1.6 microg/ml; 1.5+/-0.2 vs. 8.9+/-1.0 microg/ml; 1.5+/-0.2 vs. 8.7+/-0.5 microg/ml; 1.5/-0.2 vs. 3.5+/-0.12 microg/ml; P < 0.001). The results indicated that K562 and Raji cells were more sensitive to emodin treatment. Cell viability test indicated that inhibitory effect of emodin on various tumor cell lines was not through direct cytotoxicity. It suggested P. hypoleucum Ohwi included a tumor cell growth inhibitor.