Background Integrase interactor 1 (INI1), which encodes a component of the ATP-dependent chromatin remodeling hSWI-SNF complex, has been identified as a tumor suppressor in many tumors. Nonetheless, the role of INI1 in gastric tumor progression is not known exactly. The aim of this research was to investigate the effect of INI1 in the carcinogenesis and progression of gastric cancer. Methods Gastric tumor tissues with different differentiation levels from clinical gastric carcinoma samples and adjacent control normal tissues were taken. Expression levels of INI1 were detected by quantitative reverse transcriptation-polymerase chain reaction (RT-PCR) and Western blotting. Gastric cancer cell line SGC7901 was transfected with INI1 eukaryotic expressing vector INI1-GFP. Cell proliferation activities were assessed by MTT; cell count and cell cycle were detected by flow cytometry (FCM); cell apoptosis were measured by TUNEL and FCM; cell migration and invasiveness were evaluated by wound healing and transwell assays. Expression levels of INI1 and proliferation-related genes including p16, p21, cyclin D1 and cyclin A, apoptosis genes p53, B-cell non-Hodgkin lymphoma-2 (Bcl-2), Bcl-2-associated x protein (Bax) and caspase-3, and invasion-related genes including intercellular adhesion molecule 1 (ICAM1), matrix metalloproteinase 2 (MMP2), MMP9 and tissue inhibitor of matrix metalloproteinase 1 (TIMP1), were detected by quantitative RT-PCR and Western blotting. Results INI1 expression levels were lower in gastric carcinoma compared with adjacent control normal tissues. Overexpression of INI1 in SGC7901 cells inhibited its proliferation and invasiveness, but increased anoikis and G(0)/G(1) cell number. INI1-GFP transfection upregulated expression of INI1 and proliferation related genes p16 and p21, apoptosis genes p53 and Bax, and invasion-related genes TIMP1; cyclin D1, cyclin A, Bcl2, ICAM1, MMP2 and MMP9 were downregulated, and there was no significant change in caspase 3 levels. Conclusion INI1 plays a key role in gastric carcinogenesis by affecting proliferation, apoptosis and invasion. Chin Med J 2012;125(3):527-532