Colon cancer develops over a period of 10 to 15 years, providing a window of opportunity for chemoprevention and early intervention. However, few molecular targets for effective colon cancer chemoprevention have been characterized and validated. Protein kinase CBII (PKCBII) plays a requisite role in the initiation of colon carcinogenesis in a preclinical mouse model by promoting proliferation and increased B-catenin accumulation. In this study, we test the hypothesis that PKCBII is an effective target for colon cancer chemoprevention using enzastaurin (LY317615), a PKCB-selective inhibitor, in a mouse model of colon carcinogenesis. We find that enzastaurin potently reduces azoxymethane-induced colon tumor initiation and progression by inhibiting PKCBII-mediated tumor cell proliferation and B-catenin accumulation. Biochemically, enzastaurin reduces expression of the PKCBII-and B-catenin/T-cell factor-regulated genes PKCbII, cyclooxygenase II , and vascular endothelial growth factor, three genes implicated in colon carcinogenesis. Our results show that enzastaurin is an effective chemopreventive agent in a mouse model of sporadic colon cancer that significantly reduces both tumor initiation and progression by inhibiting expression of proproliferative genes. Thus, PKCBII is an important target for colon cancer chemoprevention and the PKCB-selective inhibitor enzastaurin may represent an effective chemopreventive agent in patients at high risk for colon cancer.