The purpose of this study was the effectiveness of social stories intervention on aggressive behavior of aggressive preschool children. The preschool aggression scale was distributed among the teachers to complete it for all 4-5 year old children in 2 kindergartens. Based on teachers' ratings of children's aggressive behavior, those who scored more than 125.77 for boys and more than 117.48 (Vahedi, Fathiaza, Hosseini-Nasab, Moghaddam, 2008) for girls, a 14 subject sample size (7 subjects in each group) was determined for the present study. Aggression Scale for Preschoolers (Shahram Vahedi et al., 2008) was employed for data collecting and analyzing. Z Value results for the differences in post-test mean rank scores between experimental and control groups on Aggression Scale for Preschoolers. The table shows that (Z) values were (-2.232) for verbal aggression, (-2.431) for physical aggression, (-2.301) for relational aggression, (-2.455) for impulsive anger, and (-2.661) for the composite score. These values are significant at the level (0.01, p< 0,01 ) in the favor of the treatment condition. The second objective of the study was to determine the effect of social stories on decreasing aggressive behaviour in aggressive preschool children. The treatment consisted of aggressision training through use of social stories. The children's performance on aggression was measured pre and post intervention. The table shows that (Z) values were (-2.447) for verbal aggression, (-2.561) for physical aggression, (-2.423) for relational aggression, (-2.401) for impulsive anger, and (-2.546) for the composite score. These values are significant at the level (0.01, p< 0,01 ) in the favor of post testing.