AIM: To investigate the effect of angiopoietin-1 (Ang-1)on biological behaviors in vitro and tumorigenesis and angiogenesis in vitro of human gastric cancer cells.METHODS: Human full-length Ang-1 gene was cloned from human placental tissues by RT-PCR method.Recombinant human Ang-1 antisense eukaryotic expression vector was constructed by directional cloning,and transfected by lipofectin method into human gastric cancer line SGC7901 with high Ang-1 expression level.Inhibition efficiency was confirmed by semi- quantitive PCR and Western blot method. Cell growth curve and cell cycle were observed with MTT assays and flow cytometry, respectively. Nude mice tumorigenicity test was employed to compare in vitro tumorigenesis of cells with Ang-1 suppression. Microvessel density (MVD) of implanted tumor tissues was analyzed by immunohistochemistry for factor Ⅷ staining.RESULTS: Full-length Ang-1 gene was successfully cloned and stable transfectants were established,namely 7Ang1- for antisense, and 7901P for empty vector transfected. 7Ang1- cells showed down-regulated Ang-1 expression, while its in vitro proliferation and cell cycle distribution were not significantly changed.In contrast, xenograft of 7Ang1- cells in nude mice had lower volume and weight than those of 7901P after 30 days implantation (P＜0.01, 293.00±95.54 mg vs. 624.00±77.78 mg) accompanied with less vessel formation with MVD 6.00±1.73 compared to 7901P group 8.44±1.33 (P＜0.01).CONCLUSION: Ang-1 may play an important role in tumorigenesis and angiogenesis of gastric cancer, and targeting its expression may be beneficial for the therapy of gastric cancer.