Purpose: This qualitative study aimed to understand and describe teachers' experiences of early childhood sex education. Methods: For data collection, in-depth interviews were conducted with 18 early childhood teachers working at daycare centers until the data were saturated. Recorded interviews were transcribed verbatim. The data were analyzed using the qualitative thematic analysis method suggested by Braun and Clarke. Results: Although early childhood teachers recognized the necessity of sex education for children, they experienced difficulties in imparting sex education in daycare centers. Teachers lacked confidence because they themselves had not received proper education related to teaching sex education. It was confirmed that sex education methods and materials were lacking and outdated, and the support of educational institutions was insufficient. Teachers emphasized the importance of communication and cooperation with parents when sexual behavior problems occur in children. Conclusion: Systematic education for teachers and parents is required to raise awareness of sex education and to communicate smoothly among them.