Beta-Catenin is a critical transducer of the Wnt signal pathway and plays an important role in many developmental and cellular processes. Deregulation of beta-catenin signaling has been observed in a broad range of human tumors. In this report, we investigated whether tyrosine kinase inhibitor STI-571 could inhibit the beta-catenin signaling activity and hence suppress cell proliferation. Our results demonstrated that STI-571 effectively inhibited the constitutive activity of beta-catenin signaling in human colon cancer cells as well as the Wnt1-induced activation of beta-catenin signaling in HOS, HTB-94, and HEK 293 cells. Furthermore, STI-571 was shown to effectively suppress the proliferation of human colon cancer cells. Finally, we demonstrated that the Wnt1-mediated activation of a GAL4-beta-catenin heterologous transcription system was effectively inhibited by STI-571. Thus, our findings suggest that tyrosine phosphorylation may play an important role in regulating beta-catenin signaling activity, and inhibition of this signaling pathway by STI-571 may be further explored as an important target for alternative/adjuvant treatments for a broader range of human cancer.