Abstract: In the last few years, the incidence of allergic diseases has been rising constantly, which lead to huge damage to children's life quality and socio-economic benefits. The occurrence of allergic diseases in early life not only exerted negative influence on children's physical and mental health, but also might turn into a risk factor for allergic diseases in adulthood. Therefore, the prevention of allergic diseases in childhood is of great significance to the public health. There are evidence showing that the exposure of polyunsaturated fatty acid in early life can influence the development of allergic diseases. However, the related mechanisms have not been fully elucidated. The effect of different dose, timing and duration of exposure to polyunsaturated fatty acid on allergic diseases are still unclear. In this review, we would present the available information on the relationship of exposure to polyunsaturated fatty acid early in life and childhood allergic diseases and its related mechanisms.