Aloe-emodin is a novel active compound found in the root and rhizome of Rheum palmatum. To investigate the effects and mechanisms of aloe-emodin on human gastric cancer, MGC-803 cells were treated with 2.5, 5, 10, 20 and 40 microM aloe-emodin for 1-5 d. The results showed that aloe-emodin inhibited the growth of cancer cells in a dose-dependent manner with an increase in S phase and in the proportion of cells cycling at a higher ploidy level >>G2/M). Moreover, the alkaline phosphatase (ALP) activity, an indicator of cell differentiation, was found decreased. This is one of the first to focus on the effect of ALP activity in human gastric carcinomas cells treated by aloe-emodin. These results indicate that aloe-emodin has a potential value for the treatment of gastric cancer and its mechanisms are by means of cell cycle interruption and induce differentiation.