The unique physicochemical properties of nanoparticles (NPs) make them widely used in cosmetics, medicines, food additives, and antibacterial and antiviral compounds. NPs are also used in therapy and diagnostic applications. Depending on their origin, the NPs are commonly classified as naturally occurring and synthetic or anthropogenic NPs. Naturally occurring nanoparticles can be formed by many physical, chemical, and biological processes occurring in all spheres of the earth. However, synthetic NPs are specifically designed or unintentionally produced by different human activities. Owing to their nano size and special properties, the engineered NPs can enter the human body through different routes such as dermal penetration, intravenous injection and inhalation. NPs may accumulate in various tissues and organs including the brain. Indiscriminate use of NP is a matter concern due to the dangers of NP exposure to living organisms. It is possible for NPs to cross the placental barrier, and adversely affect the developing fetus, posing a health hazard in them by causing neurodevelopmental toxicity. Thus, NP-induced neurotoxicity is a topic that demands attention at the maternal-fetal interface. This chapter summarizes the routes by which NPs circumvent the blood-brain barrier, including recent investigations about NPs’ neurotoxicity as well as possible mechanisms involved in neural fetotoxicity.