This research was conducted to investigate the individual and organizational effects of school administrators' toxic leadership behaviors, according to teachers' opinions. The research was carried out using the phenomenology pattern included in the qualitative research tradition. The research was carried out in preschool, primary, secondary and high school schools in Kocaeli province Kartepe district in the 2021-2022 academic year, and the opinions of twenty teachers were consulted in order to find answers to the research questions. The research data was determined by using criterion sampling and snowball sampling from purposive sampling methods. Descriptive analysis and content analysis methods, which are one of the qualitative data analysis techniques, were used in the analysis of teachers' opinions. According to the findings, toxic behaviors of school administrators; behaviors that prevent communication, behaviors that do not comply with managerial ethics, authoritarian behaviors, negative moods, unreliable behaviors, narcissistic behaviors, selfish behaviors and self-interested behaviors are collected in eight sub-themes. It has been revealed that many negative behaviors that school administrators constantly and intensely exhibit are perceived as toxic by teachers. It has been seen that school administrators' use of commanding, scolding and non-polite spoken language, unjust practices and behaviors, trying to manage by spreading fear, strict and oppressive attitudes, imposing their own ideas, and being unreliable have a significant toxic effect on teachers. It has been determined that toxic leadership behaviors of school administrators have individual effects on teachers' emotional state, mental health, thoughts and behaviors, and physiological structure. The results of the research revealed that toxic leadership behaviors of school administrators can cause physiological problems such as fatigue, weakness, insomnia, headache, loss of appetite and weight loss. The results obtained in the research indicate that the toxic leadership behaviors exhibited by school administrators have negative effects both in the short and long term. It has been determined that toxic leadership behaviors of school administrators have effects on the order and functioning of the organization, organizational trust, organizational behaviors, organizational communication, organizational conflict, and organizational goals at the organizational level. It has been determined that toxic leadership behaviors of school administrators lead to the formation of an unfair order, the dominance of authoritarian mentality, and the damage to trust in administrators in schools. Suggestions were made to practitioners and researchers within the framework of the findings.