This research aims to determine the perceptions of teachers working at various levels of formal education in Turkey towards in-service training activities. The case study design, one of the qualitative research designs, was used in the research. The research was conducted in the fall semester of the 2021-2022 academic year, using a semi-structured interview form with a total of 56 teachers working at various levels in public schools in Erzurum city and voluntarily supporting the research. In the analysis of the data obtained from the research process, both descriptive and content analysis methods were used together. When the results obtained from the research are examined, it is seen that a significant part of the teachers do not find the in-service training activities they participate insufficient in terms of scope and content, and they prefer in-service training on subjects such as information technologies, special education, training coaching, developmental psychology, teaching methods and techniques, software and material preparation. They stated that they prefer to attend on-the-job training activities mostly voluntarily and by using face-to-face training methods.