Inhibitor　of　growth　1b　(ING1b)　is　considered　to　be　a　class　II　tumor　suppressor　gene.　Although　decreased　expression　of　p33＜sup＞ING1b＜/sup＞　has　previously　been　reported　in　colorectal　cancer　(CRC),　its　role　in　CRC　has　remained　to　be　elucidated.　The　present　study　was　designed　to　assess　the　function　of　p33＜sup＞ING1b＜/sup＞　in　CRC　and　to　further　evaluate　its　underlying　mechanisms　of　action.　Western　blot　analysis　confirmed　that　ING1b　gene　expression　was　significantly　decreased　in　CRC　tissues　compared　with　that　of　adjacent　non-tumorous　colorectal　tissues.　Furthermore,　recombinant　adenovirus-mediated　ectopic　expression　of　p33＜sup＞ING1b＜/sup＞　resulted　in　growth　inhibition,　G1-phase　cell　cycle　arrest　and　apoptosis　in　the　SW480,　HT29　and　LoVo　colorectal　adenocarcinoma　cell　lines.　The　results　suggested　that　the　downregulation　of　ING1b　contributes　to　colorectal　carcinogenesis　and　that　ectopic　expression　of　ING1b　may　be　a　potentially　useful　therapeutic　approach　for　CRC.