Abstract: AIM　To study the apoptosis-inducing and growth-inhibitory effect of rhein, an herb-derived compound, and its combination with mitomycin C (MMC) on cultured tumor cells. METHODS　MTT assays were used to determine the inhibition of proliferation by drugs in several tumor cell lines. Nucleoside transport and DNA synthesis inhibition were determined by ［³H］ thymidine transport and incorporation assays. Flow cytometry, electrophoresis on agarose gels and morphological assesment were applied to analyze the apoptotic changes. RESULTS　The IC₅₀ values of nucleoside transport was 19.1 μg·mL^-1 and that of the DNA synthesis inhibited by rhein was 27.4 μg·mL^-1. In MTT assay the IC₅₀ values of rhein for KB, hepatoma BEL-7402 and mammary carcinoma MCF-7 cells were 11.5 μg·mL^-1, 14.0 μg·mL^-1 and 18.4 μg·mL^-1 respectively. Synergistic effect of rhein and MMC was found in all the three cell lines. As found, rhein induced apoptosis in KB cells, and the increase of apoptotic cells reached 71.0% at 96 h. The combination of rhein and MMC enhanced the induction of apoptosis significantly. CONCLUSION　These results suggest that rhein, as a biochemical modulator, might be potentially useful in cancer chemotherapy.