In the scope of behavioral research, examining the role of developmental and cognitive factors on bullying behaviors has been emphasized. However, there is no comparative study to investigate self-understanding among adolescent bullies and normal peers. The present study aimed to compare the developmental levels of self-understanding (self-as-subject and self-as-object) in adolescent bullies and normal peers. In a causal-comparative design, 120 adolescents were chosen by multi-stage cluster random sampling and screening method. Olweus Bullying Scale (1996), self-understanding interview and teachers' nominations were used to gather the data. The results of Chi squares test showed that in self-as- object domain, referring to physical and active schemas were more in adolescent bullies (χ2 = 60.94,  p<0.01).  In self-as-subject domain, developmental levels of continuity (χ2 = 35.43, P>0.01), distinctness
(χ2 = 43.42 , P>0.01) and volition(χ2 = 9.08 , P>0.01) were higher in normal adolescents than bullies. Implications of this study regarding the developmental role of self-understanding in bullying behaviors on one hand and planning intervention programs based on adolescents’ developmental aspects on the other hand are considered..