Preschool period is important for the development and socialization of children. In this period when children's behavior is shaped, they can learn positive or negative behavior from their social environment. This study is carried out to determine the opinions of preschool teachers regarding the aggressive behavior of their students, and one of the qualitative research methods; the case study model, and semi-structured interview technique is also used as a data collection tool. The sample of the study consists of 10 teachers working in preschool education institutions in Körfez which is a district of Kocaeli city in Turkey in 2019-2020 academic year. Descriptive analysis method is used to analyze the data obtained from the interview’s form applied to teachers. As a result of the research, the type of aggression observed in pre-school students is mostly physical; it is concluded that one of the most important reasons for students to show aggressive behavior is due to the fact that children only care about their own wishes. Teachers' method of coping with these behaviors, is to talk to the student and understand the problem. Aggressive behavior is observed more often in boys, in terms of gender and when the reactions of the friends of these students who show aggressive behaviors are observed, they prefer to stay away from their friends or display the same behavior. When the effect of the families are investigated, the students who are exposed to aggressive behaviors and wrong parent attitudes by their parents mostly behave aggresively