Although glycogen synthase kinase-3 (GSK-3) might act as a tumor suppressor since its inhibition is expected to mimic the activation of Wnt-signaling pathway, GSK-3beta may contribute to NF-kappaB activation in cancer cells leading to increased cancer cell proliferation and survival. Here we report that GSK-3beta activity was involved in the proliferation of human ovarian cancer cell both in vitro and in vivo. Inhibition of GSK-3 activity by pharmacological inhibitors suppressed proliferation of the ovarian cancer cells. Overexpressing constitutively active form of GSK-3beta induced entry into the S phase, increased cyclin D1 expression and facilitated the proliferation of ovarian cancer cells. Furthermore, GSK-3 inhibition prevented the formation of the tumor in nude mice generated by the inoculation of human ovarian cancer cells. Our findings thus suggest that GSK-3beta activity is important for the proliferation of ovarian cancer cells, implicating this kinase as a potential therapeutic target in ovarian cancer.