Abstract: Objective To study the anti-tumor effects of citrate combined with arsenic trioxide on human gastric cancer cell in vitro and possible mechanism. Methods Citrate (final concentration of 5 mmol / L) and (or) different concentrations of As₂O3 (final concentration was 5 or 10 μmol / L) treated in vitro cultured gastric cancer cell line SGC-7901 and BGC-803.Flow cytometry was used to detect apoptosis and cell cycle changes.The apoptosis-related gene Bcl-2 and Mcl-1 expressions were identified by RT-PCR to observe. Results Citrate combining with As₂O3 had a stronger inhibition function on human gastric cancer cell line compared with citrate or As₂O3(P<0.05) alone.Compared with blank group, the cell cycle distribution was arrested at G₂ / M phase, and the proportion of G0/G1 phase cell decreased and G2/M phase increased (P<0.05).The expression of bcl-2 and mcl-1 was significantly decreased（P<0.05）. Conclusion Citrate combining with As2O3 had the synergistic effects on gastric cancer cell.The mechanism might be related to cell cycle blocking and apoptosis-inducing effects through bcl-2 and mcl-1 genes.