Methylmercury is a neurotoxic environmental pollutant which can cause irreversible damage to the central nervous system. Docosahexaenoic acid (DHA) is an n-3 polyunsaturated fatty acid, an important component for the growth of nerve cells. Many studies have found that DHA can protect against neuronal damage caused by methylmercury, but the mechanism is still not clear. Firstly, this paper introduced the neurotoxicological mechanism of methylmercury and clarified the neurological damage of methylmercury on humans. Secondly, this paper introduced proposed potential mechanism of DHA on methylmercury-induced neurotoxicity, and concluded that DHA can protect neurons through enhancing cell antioxidant capacity, reducing the absorption of methylmercury by cells, balancing intracellular and extracellular calcium levels, and changing cytoskeleton. Therefore, methylmercury exposure should be avoided during critical periods of development, and DHA supplementation may assist normal development of the nervous system. Finally, this paper proposed that we should pay attention to the effects of polyunsaturated fatty acids on methylmercury neurotoxicology and underlying mechanisms, and explore a new direction for studies on the protection of neuronal damage caused by methylmercury.