The purpose of this study is to determine the teachers' views about the effectiveness of in-service training seminars held in September and June, and the difficulties encountered in these seminars. In the study in which survey method is used the data were gathered from teachers who were working in different school types in Pendik, İstanbul. The teachers’ view survey about in-service training seminars held in September and June was used as the data collection tool. Descriptive statistics were used in the analysis of the quantitative data obtained. According to the results of the study, teachers think that the topics “Curriculum and Legislation”, “Work of the Teachers from the Same Branches”, "Annual Working Programs and Planning" and "Other Topics Determined by Administrators" provide moderate benefit and above. According to teachers, the most common difficulties in seminars are; lack of motivation in seminars, lack of well-planned work and deficiency of the materials to be used in seminars. The prominent recommendations of the teachers’ for the development of the seminars are appointment of the expert trainers to in-service trainings, updating the topics, taking the needs of the teachers into consideration when the topic is determined, giving practical trainings and increasing the work done with the teachers from the same branches.