Objective To investigate the role of β-catenin gene in breast tumorigenesis by detecting mutation and expression of β-catenin gene in breast hyperplasia and breast cancer. Methods Mutation and expression of β-catenin gene in 42 breast cancer, 15 simple hyperplasia and 15 atypical hyperplasia were detected by polymerase chain reaction-single strand conformation polymorphism and immunohistochemistry. Results Normal expression of β-catenin occurred in tissue of breast simple hyperplasia. The rate of abnormal expression of β-catenin in tissue of breast atypical hyperplasia and breast cancer were 26.7% （4/15） and 59.5% （25/42）, respectively, which were higher than that of simple hyherplasia tissue (P＜0.05). And there was a markedly difference between the atypical hyperplasia tissue and breast cancer tissue (P＜0.05). Mutation of β-catenin gene wasn’t detected in this three kinds of tissues. Conclusion Abnormal expression of β-catenin plays an important role in human breast tumorigenesis, reason of abnormal expression of β-catenin isn’t mutation of β-catenin gene. Expression of β-catenin can be regulated by other mechanisms.