Sex education in primary schools aims to prevent sexual harassment and provide knowledge to students. Sex education for students in schools is the responsibility of the school, so teachers need to understand sex education and how to provide sex education in schools. This study aims to determine the knowledge of teachers about sex education at SD Negeri 2 Sudagaran. This research uses a qualitative descriptive research approach. Participants in this study were teachers in fifth and sixth grades using an open questionnaire and interview data collection. Test the validity of the data in this study using triangulation techniques. Based on the results of the study, it was obtained that the knowledge of teachers about sex education at SD Negeri 2 Sudagaran was adequate according to the basic concepts of sex education in primary schools. Teachers' knowledge about sex education concerns understanding sex education, the importance of sex education in primary schools, sex education materials, triggers for sexual harassment, and efforts to prevent sexual harassment.