The purpose of this study is to examine pedagogical content knowledge of preschool teachers in social studies. To achieve this purpose, a total of forty-nine participant observations and in-depth interviews were conducted in addition to collection of documents. Three teachers teaching four-year-old children at a daycare center and one teacher teaching five-year-old children at a kindergarten participated. Data analysis suggests that four pedagogical domains contribute to effective social studies teaching: content knowledge of social studies, knowledge of children, general pedagogical knowledge, and social and cultural knowledge. With regard to content knowledge of social studies for young children, the content of executed social studies was much more than one of the planned by teachers in its amount and categories. So, teachers should consider null curriculum. Regarding general pedagogical knowledge, the teachers used the class-control skills for more effective class-control. In regard to the knowledge of children, the teachers considered misconceptions and unique conditions of each individual of child in executing the activities of the social studies. Regarding social and cultural knowledge, the teachers considered social factor as other class children, the director of the daycare center or the kindergarten, and the parents of the children and cultural factor as English. So, the components of pedagogical content knowledge in social studies for young children are four knowledge, and good teachers would know well about all the areas of social studies pedagogical content knowledge.