BACKGROUND: Adolescent sexual debut and non-consensual sex have been linked to higher sexual risk and STI infection in adulthood among men who have sex with men (MSM) in high-income countries. This study aimed to examine adolescent and non-consensual anal sexual debut among Chinese MSM and to evaluate factors associated with adolescent sexual debut and non-consensual anal sex. METHODS: A cross-sectional study was conducted recently among Chinese men assigned male sex at birth, ≥18 years old, and who had ever engaged in anal sex with a man. Participants answered questions regarding socio-demographics, condomless sex, age at anal sexual debut with a man, and whether the first anal sex was consensual. Factors associated with an adolescent sexual debut (< 18 years old) and non-consensual sex at sexual debut were evaluated. We defined adolescent sexual debut as having anal sex with another man at 17 years old or younger, and the participants were asked whether their first male-to-male anal sex was non-consensual. RESULTS: Overall, 2031 eligible men completed the survey. The mean age of sexual debut was 20.7 (SD = 4.3) years old. 17.6% (358/2031) of men reported adolescent sexual debut, and 5.0% (101/2031) reported a non-consensual sexual debut. The adolescent sexual debut was associated with having more male sexual partners (adjusted OR 1.10, 95% CI 1.06-1.15) and condomless anal sex in the last three months (AOR = 1.71, 95% CI 1.34-2.18). MSM whose sexual debut was non-consensual were more likely to have condomless anal sex (AOR = 1.76, 95% CI 1.17-2.66), and to have reported an adolescent sexual debut (AOR = 2.72, 95% CI 1.75-4.21). CONCLUSIONS: Many Chinese MSM reported adolescent sexual debut and non-consensual sex, both of which are associated with sexual risk behaviors and drive STI transmission. These findings highlight the need for designing tailored interventions for MSM who experienced adolescent sexual debut and non-consensual sex at debut.