Inhibitor　of　growth　1b　(ING1b)　is　considered　to　be　a　class　II　tumor　suppressor　gene.　Although　reduced　expression　of　p33(ING1b)　has　been　reported　in　many　human　malignancies,　including　gastric　cancers,　the　effect　of　p33(ING1b)　on　gastric　cancer　cells　has　yet　to　be　investigated.　Expression　of　p33(ING1b)　in　gastric　adenocarcinoma　tissues　and　their　adjacent　non-malignant　gastric　mucosa,　as　well　as　in　gastric　adenocarcinoma　cell　lines　and　normal　gastric　epithelial　cells,　was　detected　by　using　Western　blotting.　Recombinant　adenoviruses　were　prepared　to　mediate　the　ectopic　expression　of　p33(ING1b)　(Ad-ING1b)　and　green　fluorescent　protein　(GFP)(Ad-GFP)　in　the　gastric　adenocarcinoma　cell　lines,　SGC-7901,　MKN28,　and　MKN45　and　the　normal　gastric　epithelial　cell　line　GES-1.　Alterations　in　the　proliferation　and　apoptosis　of　the　cells　after　adenoviral　infection　were　determined　by　the　3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium　bromide　(MTT)　assay　and　flow　cytometry,　respectively,　and　cell　cycle　distribution　was　analyzed　in　a　fluorescence-activated　cell　sorter.　Western　blotting　confirmed　the　reduced　expression　of　p33(ING1b)　in　gastric　adenocarcinoma　tissues　and　gastric　adenocarcinoma　cell　lines.　The　ectopic　expression　of　p33(ING1b)　mediated　by　Ad-ING1b　resulted　in　decreased　growth,　increased　apoptosis,　and　cell　cycle　arrest　at　the　G1　phase　in　both　benign　and　malignant　gastric　epithelial　cells　regardless　of　their　p53　status.　Addition　of　a　p53　inhibitor,　pifithrin-alpha,　did　not　abolish　the　pro-apoptotic　and　cell　cycle-arresting　effects　of　p33(ING1b)　in　p53　wild-type　cells.　Down-regulation　of　p33(ING1b)　might　play　an　important　role　in　the　development　of　gastric　adenocarcinoma.　Targeted　local　expression　of　p33(ING1b)　may　offer　a　promising　alternative　therapeutic　measure　for　gastric　cancer.