Objective To explore the effects of morphine on biological characters of human gastric carcinoma cell line MGC-803. Methods MGC-803 cells were incubated with 0.1,10 or 1000 μmol/L morphine. The viability of cells was determined by MTT assay at 12, 24, 36, 48, 60, 72 h after being incubated with morphine and the proliferation of cells was measured by colony formation assay 7 days later.The cell cycle progression and apoptosis were assessed by flow cytometry. The ultrastructural changes of MGC-803 cells were observed under the transmission electron microscopy. Results The proliferation of MGC-803 cells was inhibited after incubation with morphine. Clones of gastric carcinoma cell line MGC-803 in morphine groups were fewer than those in control group. In morphine groups, the proportion of cells in G2/M was higher than that in control group. In morphine groups, apoptotic rate of MGC-803 cells was higher than in control group. Moreover, apoptotic bodies were observed in morphine groups. Conclusion Morphine can effectively inhibit growth and proliferation of gastric cancer cells and may be used as a potent therapy for gastric cancer. Key words: Morphine; Gastric carcinoma; Cell proliferation