To examine pathologically the influence of diesel exhaust (DE) exposure on fetal nervous system development, brain tissue (cerebral cortex and hippocampus) was collected from newborn mice whose mothers were exposed to DE during pregnancy. After DE exposure, these brain tissues showed evidence of numerous caspase 3-positive cells (a common enzymatic biomarker of apoptosis). Some cells were found to contain crescent-shaped spaces, which are suggestive of apoptotic processes. Granular perithelial (GP) cells, scavenger cells surrounding cerebral vessels of the blood-brain barrier, showed signs of apoptosis; furthermore, the GP cytoplasmic granules had degenerated and showed evidence of what appeared to be ultrafine, DE particles. Additionally, the swelling of astrocyte endfoot that surround capillaries showed degenerative changes similar to myelin figures. Furthermore, the apoptosis of endothelial cells and stenosis of some capillaries were observed. These findings varied in severity, depended on DE concentration, and were not observed in the control group. These observations suggest that exposure of pregnant mice to DE might carry a risk of cellular atrophy and might affect fetal brain development. Our findings also reveal that inhalation of DE might be hazardous to the general health of fetuses.