The aim of this study was to investigate the expression of matrix metalloprotease-7 (MMP-7) in each component of uterine carcinosarcoma. Surgical specimens of primary tumors of uterine carcinosarcomas were obtained from 13 patients. The carcinomatous component consisted of adenocarcinoma with or without squamous differentiation. The sarcomatous component consisted of spindle cell sarcoma, chondrosarcoma and rhabdomyosarcoma, either alone or in combination. The immunohistochemical expression of MMP-7 protein was examined using the avidin-biotin peroxidase complex technique employing the anti-MMP-7 monoclonal antibody. Expression of MMP-7 protein was detected in 9 (69.2%) of 13 adenocarcinoma components, while no staining was observed in any of the sarcomatous components examined. There was a statistically significant difference of the positive rate for MMP-7 between epithelial components and sarcomatous components of uterine carcinosarcoma (p<0.01). In some cases, MMP-7 was abundantly expressed at the invasive front of adenocarcinomas. It is concluded that MMP-7 protein is differentially expressed between the carcinomatous component and the sarcomatous component of uterine carcinosarcoma. Each component of carcinosarcoma may have its own potential for invasion and metastasis. MMP-7 may contribute to the invasive nature or growth capacity of the carcinomatous component of uterine carcinosarcoma, while it may not have a relation to that of the sarcomatous components.