Receptor-binding antigen expressed on a human uterine adenocarcinoma cell line, SiSo (RCAS1), has been reported to be a prognostic factor of various malignant tumors, and it has also been proven to induce apoptosis of lymphoid cells. However, its normal distribution and function have not yet been elucidated. The purpose of this study was to disclose the distribution of RCAS1 expression in normal female genital organs. Immunohistochemical staining using anti-RCAS1 and anti-MIB-1 antibodies was performed on 123 surgical specimens of a histologically normal uterus, ovary, or fallopian tube from 66 patients, and the apoptotic index was determined. In uterine cervical glands, the expression of RCAS1 was seen in 93% of the cases, and it was mainly localized in the superficial cervical glands. Near the areas of squamous metaplasia, RCAS1 was strongly expressed in all samples. In the uterine cervical squamous epithelium, RCAS1 was seen in 84% of cases. In the uterine corpus, RCAS1 was seen in 87% of all cases, and it was mainly expressed in the endometrial glands of basalis layer. There was significant positive correlation between age and RCAS1 expression, but no significant difference was found regarding the endometrial status and RCAS1 expression in endometrium. No significant correlation was found between RCAS1 expression and MIB-1 index/apoptotic index. RCAS1 may affect these metaplastic processes and tumor progression.