Sexual health education is mandatory in South Korea. However, gender equality, and the rights of sexuality and gender-diverse people are contentious issues in Korean society. This study describes school health teachers' experiences delivering sexual health education especially in relation to gender equality and the rights of sexuality and gender minorities. A descriptive approach based on grounded theory methodology was adopted. The participants included 23 elementary, middle, and high school health teachers certified by the Korean Institute for Gender Equality Promotion and Education. One-to-one interviews were conducted with participants. Education authorities, students, other teachers, and parents create challenges for health teachers because of the tension between gender-sensitive and conservative perspectives on sexual health education. Social factors influencing these challenges include patriarchy, cultural misunderstandings regarding sexuality, conflicts between feminism and anti-feminism, heterosexual familism, and homophobia. Teachers' strategies to overcome these challenges include improving personal understanding, skills and attitudes, and asking other teachers and parents for their support. Addressing gender equality and power is the key to improving students' sexual and reproductive health. Educational authorities and civil society should support school health teachers' efforts to advance gender equality and prevent sexuality and gender identity-based discrimination.