Most of perinatological phenomenona and diseases are closely related with immune reaction. Most of initial immune responses occur through innate immunity and most causes, such as mechanical damage, hypoxia, and hyperoxia, are self and microorganisms are non-self, all of which are related with immune reaction concept. However, researches on perinatology are mainly focused on specific one or two causes of perinatal diseases, so often there is limitation to understand the basic concepts and phenomenona of the perinatal diseases. Through understanding of immune reaction concept, we can apply immune reaction theory to researches in perinatology and we can understand phenomenona in perinatology through knowledge of immune reaction. Therefore it is essential to understand historical development of immunology and concept of immune reaction for researches and treatment of perinatology.