This research was conducted to reveal, according to the opinions of the principals, the reasons for the unethical behavior of teachers towards students, colleagues, parents and school administrators while performing their profession. The research was conducted using the case study design within the qualitative research tradition. The research was conducted in high school schools in Düzce province in the 2021-2022 academic year, and the opinions of seventeen school principals were consulted to find answers to the research questions. The study group was determined using criterion sampling and snowball sampling, which are purposeful sampling methods. Descriptive analysis and content analysis methods, which are qualitative data analysis techniques, were used to analyze the school principal's opinions. According to the findings, the reasons for teachers' unethical behavior are; They were grouped into three sub-themes: reasons arising from professional inadequacy, reasons arising from the system and management, and personal reasons. Recommendations were made to practitioners and researchers within the framework of the findings.