This study is to establish if there is a connection between the maladjustment behavior of mentally retarded identical twins and hereditary transmission, and whether behavioral tr eatment results in similar effects in twins. Three male mentally retarded identical twins sc hooling in E special middle school for the mentally retarded, were selected for the study. The Individualized Education Program (IEP) and the health records of the twins were ana lyzed, and the maladjustment behaviors of the twins were recorded by the class teachers, occupational teachers and the parents of the twins. The maladjustment behavior in the twi ns were treated with cognitive behavioral treatment and behavioral treatment so that the twins would have more self-esteem, not move away from their seats and refrain from eati ng non-edible substances. From the results of the study, it was observed that the social quotient and physical conditions were influenced by hereditary transmissions and there we re many common maladjustment behaviors. The type of maladjustment behaviors in the t wins were similar but there were individual differences in the extent and effects of the be haviors. Therefore, the results of the study show that the social quotient of mentally retar ded identical twins and the maladjustment behaviors in the twins are partially influenced by hereditary transmissions, but there are differences in developmental characteristics of i ndividual twins.