Objective: To investigate the expression of apoptosis related genes p53 and bcl-2 in atypical hyperplasia of mammary duct and the relationship between the gene expression and oncogenesis of breast. Methods: mRNA of apoptosis related gene p53 and bcl-2 were detected by in situ hybridization in 44 cases of atypical ductal hyperplasia. p53 protein expression was detected by immunohistochemistry. The data were compared with those of 6 cases of benign hyperplasia and 26 cases of breast carcinoma. Results: The expression of p53 mRNA was 66.7% in benign hyperplasia, 40% in atypical ductal hyperplasia (55.6% in mild, 41.7% in medium, 26.1% in severe) and 19.2% in carcinoma (of which 21.4% were intraductal carcinoma and 16.7% were invasive). The expression of p53 protein was negative in benign hyperplasia, 24% in atypical hyperplasia (mild 11.1%, medium 25%, severe 34.8%), 38.5% in carcinoma (intraductal carcinoma 35.7%, invasive ductal carcinoma 41.7%). The expression of bcl-2 was negative in benign hyperplasia, 78.6% in intraductal carcinoma, 83.3% in invasive ductal carcinoma. Conclusion: Loss and mutation of p53 gene and excessive expression bcl-2 mRNA were detected in severe atypical ductal hyperplasia.