Abstract: To detect the inhibition of cinobufagin (CBG) on human gastric cancer MGC-803 cells and study its anti-tumor mechanism. The inhibition of cell growth of CBG was measured by MTT assay. Morphological changes were observed by optical microscopy. Apoptosis and cell cycle distribution of MGC-803 cells were determined by flow cytometry.Apoptosis of MGC-803 cell was detected by Annexin V/PI method. Cinobufagin inhibited the growth of MGC-803 cells. MGC-803 cells treated with cinobufagin showed typical characteristics of apoptosis. The cells became round，cell detachment，membrane blebbing，and cell shrinkage with a condensed cytoplasm. A net increase in the percentage of cells at G2/M phase was encountered，and this phase was maintained throughout the treatment time. Annexin V/PI flow cytometry analysis showed that CBG can cause MGC-803 cells in early apoptosis. CBG inhibited the growth of gastric cancer MGC-803 cells，induced morphological changes，made cells arrest at G2/M phase and induced apoptosis of MGC-803. The mechanism may be related to the induction of apoptosis and cell cycle arrest.

Key words: cinobufagin; anti-tumor; apoptosis; cell cycle arrest