Abstract: Objective: To study the anti-tumor effects of arsenic trioxide combined with fluorouracil on human gastric cancer cell line SGC-7901 in vitro and the mechanisms of the regimen. Methods: The human gastric cancer cell line SGC-7901 was treated n vitro using As₂O₃ (final concentrations in order: 0.1, 0.5, 1.0μmol/L) and 5-FU (final concentration: 50mg/L) respectively alone or in combination, then the cell apoptosis rate and phases of cell cycle were determined by flow cytometry, and the expression of Bcl-2 was analyzed by immunocytochemical method (PV method). Results: Compared with As₂O₃ or 5-FU groups, As₂O₃ combined with 5-FU obviously increased the apoptosis rate of SGC-7901 (q=63.9608, 166.1758, 51.3343, P<0.01). Compared with blank group, the cell cycle distribution was altered and the ratio of S phase cell decreased (q=16.0743, 10.8805, 12.1482, P<0.01)and G₀/G₁ phase increased (q=8.7188, 9.3309, 9.8534, P<0.01). After intervened by As₂O₃ combined with 5FU, the expression of Bcl-2 was down-regulated (q=10.2801, 17.8456, 19.0086, P<0.01). Conclusion: As₂O₃ combined with 5-FUhas the synergistic effects on SGC-7901, and the mechanisms maybe related tocellcycleblockingandapoptosis-inducingeffectsthroughregulatingtheexpressionoftherelatedgenes.