Abstract: Objective To explore the relationship of abnormal expression of Skp2 and p27kip1 between intraductal proliferation lesions and breast cancer. Methods The positive expression ratio of Skp2 protein and p27kip1 protein in 30 cases of normal control group,120 cases of intraductal proliferation lesions including 30 cases of usual ductal hyperplasia (UDH),30 cases flat epithelial atypia(FEA),30 cases of atypical ductal hyperplasia(ADH) and 30 cases of ductal carcinoma in situ(DCIS) were detected using immunohistochemical method. Results The positive expression ratio of Skp2 in four subtypes were all higher than that in normal control (P<0.05).The positive expression ratio of Skp2 protein of DCIS,FEA and ADH were higher than that of UDH.There were significant difference between DCIS,FEA and ADH（P<0.05）.The positive expression ratio of p27Kip1 in four subtypes were all lower than that in normal control (P<0.05).Remarkable difference of expression ratio of p27kip1 existed between UDH and DCIS (P<0.05),FEA and DCIS (P<0.05),ADH and DCIS (P<0.05).Skp2 protein level was reversely correlated with p27kip1 protein level overall（r=-0.411,P=0.000）.The same results existed in UDH and DCIS,respectively（r=-0.406，P=0.026;r=-0.544,P=0.002）. Conclusion The increase of expression level of Skp2 protein and decrease of expression level of p27kip1 protein have closed association with dysplasia of breast ductal epithelial and development of breast cancer.