Social cognition refers to how children understand Opinions, feelings, thoughts and intentions themselves and others and how they think about social relations. Processes of social cognition, enables one to predict the behavior of others, self-control and therefore regulating social interaction. In other hand, studies indicated Children and adolescents with Down syndrome have lower performance in answer to the tasks of theory of mind as the latest research domain on the development of social cognition. However in recent years with expansion in mental retardation definition in "social competence" and "Interpersonal Skills" areas, the purpose of training these children and adolescents considered preparing to perform activities of daily living, acceptance of personal and social responsibility and training specific job appropriate with their ability, aptitude and interest. Yet success of children and adolescents with Down syndrome seems unlikely without social cognition abilities. The current study attempt While explain concept of social cognition and its functions, Review researches was conducted abut Children and adolescents with Down syndrome’s social cognition and finally Identify and introduce some of the more important Effective factors in development of social cognition in Children and adolescents with Down syndrome.