CD147 is a multifunctional membrane glycoprotein involved in tumor invasion, and is overexpressed in many solid tumors. However, the role of CD147 in breast cancer is not well understood. The aim of this study was to evaluate CD147 expression in non-invasive and invasive ductal carcinomas. We recruited 156 breast cancer patients who underwent radical operations at our hospital up until 2002. We performed immunohistochemistry on their tumor specimens, and compared these data with clinicopathological factors. We divided the patients into two groups: group A was comprised of non-invasive ductal carcinomas and group B, invasive ductal carcinomas. The CD147-positive rate was 62.8% for all patients and was higher in group B than group A. In all cases, the CD147-positive rate correlated with clinical stage, number of metastatic lymph nodes, and tumor size. These results implied that CD147 may be involved in the process of breast cancer invasion.