OBJECTIVE: Polygonum multiflorum Thunb(P. multiflorum) has been used in the treatment of diarrhea and detoxification in China. Our previous studies showed that R50 part which was separated from P. multiflorum had little toxicity to normal cells but certain toxicity to cancer cells. This study aimed to separate the component which has different effect on normal and cancer cells in R50 part and investigate its anticancer mechanisms. METHODS:Sephadex LH-20,TLC chromatography and reverse silica gel chromatography were employed to separate and purify the emodin-8-O-β-D-glucopyranoside(PMEG). The purity was evaluated by TLC and HPLC. The viability of cells treated with PMEG at different concentration and time was detected by MTT assay. Morphological changes in cells and nuclei were examined after Giemsa staining. Cell cycle and apoptosis were assayed by flow cytometry. RESULTS:The purity of PMEG separated from P. multiflorum was 96%. MTT method showed that PMEG had significant growth inhibitory effects on HepG2,HT29,and SH-SY5Y cells(P<0.05),and showed concentration dependence in HepG2 cells and HT29 cells(r=0.987,P=0.002;r=0.992,P=0.008). But PMEG had no effects on L02、HCT116 and A549 cells. PMEG (200 μg/mL) showed much more growth inhibition in HepG2 cells to L02 cells,and induced HepG2 cells apoptosis and G2-M phase block. CONCLUSION:PMEG was one of the main active anticancer component separated from R50 part of P. multiflorum,and had different effects on human liver L02 cells and liver cancer HepG2 cells,which may be related to PMEG-induced apoptosis and G2-M block in HepG2 cells.