Both genetic and environmental factors are involved in the pathophysiology of the major psychiatric disorders including schizophrenia. However, detailed molecular mechanisms are not understood. Brain‐specific somatic mutations including LINE‐1 retrotransposition are found in patients with neuropsychiatric disorders, and their patterns and frequency may play important roles in the pathophysiology of psychiatric disorders. Here we describe molecular mechanism of LINE‐1 retrotransposition and the studies of LINE‐1 retrotransposition using maternal immune activation model in mice.