Abstract: AIM: In search of antitumor biochemical modulators from traditional Chinese herbal medicines, emodin has been found to be active. The goal of present study is to investigate the effects of emodin on the nucleoside transport and multidrug resistance in cancer cells. METHODS: Nucleoside transport inhibition was determined by ［³H］-thymidine incorporation assay. The cytotoxicity to cancer cells was determined by MTT assay. The pump-efflux activity and the expression of P-glycoprotein were examined by flow cytometric assay. RESULTS: Emodin was active in the inhibition of nucleoside transport, with an IC₅₀ value of 9.9 μmol.L^-1. Emodin markedly enhanced the cytotoxicity of 5-FU, MMC and MTX against human hepatoma BEL-7402 cells and partly reversed the multidrug resistance in human breast cancer MCF-7/Adr cells. Emodin inhibited P-gp pump-efflux activity and reduced the expression of P-gp in MCF-7/Adr cells. CONCLUSION: These findings provide a biological basis for the application of emodin as a biochemical modulator to potentiate the effects of antitumor drugs and reverse the multidrug resistance in cancer cells.