Background. Nowadays, one sixth of the world’s population is represented by adolescents, nearly 1.2 billion people being of age 10-19. According to the 2011 census in Iran, the estimation of adolescent population was 12 million, which represents 16% of the Iran population. Undoubtedly, adolescence is the most dominant stage of life. During this period, adolescents face biological, cognitive, and emotional changes that may be accompanied by inappropriate behavioral responses such as aggression. Considering pressures of peer groups during adolescence, assertiveness has an important role as a social skill. It seems that the success of adolescents in dealing with these problems depends on their self-efficacy. This study was designed to explore the role of self-efficacy and assertiveness in aggression among high-school students.

Material and methods. This cross-sectional and correlational study was conducted among 321 first grade high-school students during 2014 and 2015. Samples were extracted from six education and training regions by a multi-stage random sampling. In this study, the questionnaire included demographic, Rathus Assertiveness, self-efficacy for children and aggression data.

Results. The results showed that there was a notable negative association between aggression and assertiveness (p < 0.003) and also between assault and self-efficacy (p < 0.001).

Conclusions. An increase in assertiveness and self-efficacy resulted in a decrease of aggression. So, training was recommended to reinforce self-efficacy beliefs and assertiveness behaviors for mental health promotion.