Nano-sized plastic particles formed from both daily use plastics and its debris have become a potential health and environmental problem due to features such as transportation through food webs and maternal transfer. Although many studies on the toxicity of plastics exist more detailed and molecular studies are needed to evaluate and review the effects of plastics especially in nano-size range. For this purpose, we have microinjected polystyrene nanoplastics (PNP) (20 nm) to the zebrafish embryo, which is one of the best model organisms for developmental toxicity studies, to simulate intake with food or maternal. Survival, hatching and malformations evaluated during the experimental period (120 h). Moreover, we have aimed to put forth the presence of reactive oxygen species (ROS) and apoptosis signalling accumulation in the body in addition to bioaccumulation of PNP and immunochemical toxicity (8-OHdG) on the brain of zebrafish larvae at the 120th hour. According to results, it has been demonstrated that 20 nm diameter PNP can reach the brain and bioaccumulate there, moreover lead to oxidative DNA damage in the brain regions where it bioaccumulates. Here we have also imaged the PNP from a vertebrate brain via transmission electron microscopy (TEM) for the first time. As a result of these, it has been detected increasing mortality and prevailing abnormalities in addition to excessive ROS and apoptosis in especially the brain. As a conclusion, obtained data have suggested that precautions, on the use and contamination of the plastic product, to be taken during both pregnancy and baby care/feeding are important for the health of the baby in future.