Abstract: Objective To investigate the effects of arenaria kansuensis aqueous extract (AKAE) on proliferation and cell cycle of human gastric cancer cell line MGC-803. Methods MGC-803 cells were treated with AKAE at different concentration. The effect on proliferation of MGC-803 cells was detected by MTT assay. The flow cytometry was used to test the cell cycle of MGC-803 cells. The protein and mRNA expressions of cyclin D1, p16 and p21 in MGC-803 cells were detected by western blot and real-time PCR respectively. Results The proliferation of MGC-803 cells was dose-dependently inhibited by AKAE treatment in vitro(P<0.05)，and the value of IC₅₀ was (0.134±0.005)mg/ml. After treated with AKAE at the dose of 0.8 mg/ml for 12 h, the ratio of G₁ phase in MGC-803 cell cycle was increased, and the ratio of S phase in MGC-803 cell cycle was decreased(P<0.05). The protein and mRNA expressions of cyclin D1 in MGC-803 cells were obviously blocked by AKAE at the dose of (0.2-0.8) mg/ml（P<0.05）.AKAE treatment could enhance the mRNA expressions of p16 and p21 in MGC-803 cells.Compared with control group, the relative expression values of p16 and p21 mRNA in 0.2 mg/ml group were 2.30 and 17.5 times higher, respectively. Conclusion AKAE could inhibit the proliferation of MGC-803 cells, and the mechanism is closely associated with G₁-phase cell cycle arrest and expression of G₁-phase related factors.