AbstractLiquid–liquid phase separation has emerged as an important mechanism for regulating cell activity by promoting the formation of membrane‐less condensates. In the nervous system, the formation of distinct molecular condensates via phase separation is involved in synaptic assembly and function. Disruption of phase separation is associated with several disease states, such as cancer, neurodegenerative disorders, and neurodevelopmental disorders. This review summarizes the function of phase separation in the assembly and plasticity of the synapse, discusses the role of abnormal phase separation in neurological diseases, and proposes potential treatment options for these neurological diseases based on phase separation.