Lesbian, gay, bisexual, transgender, queer, and other gender and sexually diverse (LGBTQ+) students in schools often face hostile environments marked by discrimination, exclusion, and victimization. Teachers play a critical role in shaping inclusive school climates, yet few validated tools exist to assess their engagement in LGBTQ+-inclusive teaching practices. This study aimed to develop and validate the LGBTQ+-Inclusive Teaching Scale (LITS). A total of 305 secondary school teachers in China were recruited to participate in the study. An initial pool of items was evaluated through exploratory and confirmatory factor analyses, resulting in an 8-item scale with two factors. Instructional and environmental inclusion captures structured and visible efforts to support LGBTQ+ students, while interpersonal affirmation reflects responsive and relational practices within classroom interactions. The two factors demonstrated strong internal consistency. Construct validity was supported by significant negative correlations with attitudes toward gay men. The results also showed that teachers with greater contact with sexual and gender minority individuals, more exposure to LGBTQ+ media, and more positive perceptions of student attitudes toward sexual and gender minority individuals reported higher levels of inclusive teaching practices. The LITS is a reliable and valid instrument for assessing LGBTQ+-inclusive teaching in China. It offers a comprehensive framework for evaluating and promoting inclusive practices in schools, with implications for research, professional development, and educational policy.