Background Sexualised drug use (SDU) is common in men who have sex with men (MSM). Chemsex, a form of psychoactive SDU, is a strong risk factor for sexually transmitted infections (STIs). We investigated the associations of SDU and chemsex with the sexual behaviours in Chinese MSM. Methods From 23 March 2022 to 22 April 2022, we recruited participants (male, >18 years old) via WeChat across five Chinese cities to an online cross-sectional survey on sexual behaviour preferences, pre-exposure prophylaxis, SDU, and chemsex. One-way ANOVA and chi-squared tests were used to compare sexual behaviour patterns across the groups. Results We included the responses from 796 eligible participants, who were aged 18–70 years, and mostly single. Three groups of participants were identified, the largest was the ‘non-SDU group’ (71.7%), followed by the ‘SDU without chemsex’ group (19.7%), and the ‘chemsex’ group (8.5%). Poppers (8.4%) were the most used drugs in the ‘chemsex’ group. The ‘chemsex’ group also had the highest number of sexual partners, and reported the highest frequency of self-masturbation (38.2%). The ‘chemsex’ group also exhibited the highest Shannon diversity index value of 2.32 (P = 0.03), indicating a greater diversity of sexual acts. For sequential sex act pairs, the ‘chemsex’ group was more likely to self-masturbate than perform receptive oral sex, perform receptive oral sex than self-masturbate, being masturbated or perform receptive oral sex than being rimmed by another man. Conclusion Our findings identify the urgent need for targeted HIV/STI interventions for MSM who practice chemsex.