The toxicity of nanoparticles (nanotoxicology) is being investigated to understand both the health impacts of atmospheric ultrafine particles—the size of which is a fraction (<0.1 μm aerodynamic diameter) of that of PM2.5 (<2.5 μm diameter)—and the safer use of engineered nanomaterials. Developmental toxicity of nanoparticles has been studied since their transfer from pregnant body to fetal circulation and offspring body was first reported. Here we reviewed the developmental toxicity of nanoparticles on the brain, one of the most important organs in maintenance of mental health and high quality of life. Recently the dose- and size-dependency of transplacental nanoparticle transfer to the fetus was reported. It is important to understand both the mechanism of direct effect of nanoparticles transferred to the fetus and offspring and the indirect effect mediated by induction of oxidative stress and inflammation in the pregnant body. Locomotor activity, learning and memory, motor coordination, and social behavior were reported as potential neurobehavioral targets of maternal nanoparticle exposure. Histopathologically, brain perivascular cells, including perivascular macrophages and surrounding astrocytes, have an important role in waste clearance from the brain parenchyma. They are potentially the most sensitive target of maternal exposure to low-dose nanoparticles. Further investigations will show the detailed mechanism of developmental toxicity of nanoparticles and preventive strategies against intended and unintended nanoparticle exposure. This knowledge will contribute to the safer design of nanoparticles through the development of sensitive and quantitative endpoints for prediction of their developmental toxicity.