In this paper we present the results of research on a sample of 101 children. All children attending kindergarten "Sunčica" that exists within the Public Institution for pre-school education "Our child" Tuzla. Our goal was to investigate and determine which behavior, prosocial or aggressive, is more manifested by pre-school children. Also, we wanted to determine whether there is a significant difference in the expression of aggressive and prosocial behavior of children in relation to their age and gender. The results we obtained showed that preschool children manifested more prosocial than aggressive behavior, that there are significant differences in the expression of prosocial and aggressive behavior of children in relation to sex, and that there are significant differences between certain age groups of children in the context of prosocial behavior while among some age groups in the context of prosocial behavior and among all age groups in context of aggressive behavior there were no statistically significant differences.