Objective To investigate the molecular mechanisms of effect of glycogen synthase kinase -3beta( GSK3β) on proliferation of human osteosarcoma cells .Methods Normal osteoblast hFO and osteosarcoma cell lines were examined for GSK 3βexpression and activity by Western blot and in vitro kinase assay ( NIRKA) . The effects of small molecule GSK3βinhibitors on cell proliferation and apoptosis were examined .Depletion of en-dogenous GSK3βby GSK 3βsiRNA detected the expression and phosphorylation of p 27 and its downstream cy-clinD1-CDK-Rb pathway factor by Western blot .Human osteosarcoma cell xenografts ,in athymic mice model , were treated with DMSO as control or with GSK 3βinhibitor SB-216763 or AR-A014418 by intraperitoneal in-jection,3 times a week.The tumor growth and body weight were observed in nude mice .Results Osteosarcoma cell lines showed increased GSK 3βexpression and decreased serine 9 phosphorylation compared with normal oste-oblast cells.Inhibition of GSK3βresulted in attenuated cell proliferation and increased apoptosis in most osteosar-coma cell lines in vitro and in vivo in MG 63 xenografts in rodents but not in hFOB cells .We decreased endoge-nous GSK3b activity,tumor growth was inhibited in SB216763,AR -A014418 group compared with control group.There was statistical significance(P<0.05).GSK3βinhibition in osteosarcoma cells was associated with decreased p27 expression, Rb expression and phosphorylation level of decline , CDK2, 4, 6 protein level de-creased,the upregulation of cyclin D1 expression but the phosphorylation level of no effect .Conclusion In this research,we demonstrate that deregulated GSK 3βsustains osteosarcoma cells survival through modulation of p27and cyclinD1-CDK-Rb pathway.The result will open up a potential target for clinical treatment of osteosar -coma.