The purpose of the study is to reveal the predictive effect of aggression levels of four-year-old children on their peer victimization levels and to determine their aggression levels according to gender. The sample group of the study consisted of 186 four-year-old children attending preschool education in Pamukkale district of the province of Denizli. According to the results of the study, it was found that relational and physical aggression levels of four-year-old children statistically significantly predicted their peer victimization levels. Physical aggression levels of four-year-old children showed a significant difference according to gender. It was determined that boys had higher physical aggression levels than female peers. There was no difference between genders in terms of relational aggression levels. On the other hand, it was found that boys were exposed to peer victimization more than female peers.