Diesel exhaust (DE) is a serious air pollution problem in big cities. Most suspended particulate matter (SPM) less than 2.5 μm in diameter consists of diesel exhaust particles (DEPs), which are reported to cause pulmonary carcinogenesis, allergic rhinitis, and bronchial asthma-like diseases. It has been recently reported that DE also affects the circulatory and reproductive systems. Yoshida et al. reported that mRNA expression of steroidogenic factor-1 (Ad4BP/SF-1) and of Müllerian inhibitory substance (MIS), which are essential for male gonadal differentiation, decreased significantly in male fetuses when maternal mice were exposed to DE at levels of 0.1 or 3.0 mg DEP/m³ for 8 hr per day between 2 and 13 days postcoitum (dpc). In this study, maternal mice were exposed to DE 0.1 mg DEP /m³ for 8 hr per day between 2 and 13 dpc. Expression levels of Ad4BP/SF-1 and MIS mRNA in female fetuses were not decreased. However, expression levels of bone morphogenetic protein-15, reported to be related to development of the oocyte, were significantly decreased in comparison with that in the control group. Our data suggest that female fetuses of pregnant mice exposed to DE in utero are less sensitive to the expression levels of mRNAs for Ad4BP/SF-1 and MIS compared with males and that DE may affect development of the oocyte in the female fetus.