Background: Men who have sex with men (MSM) living with HIV make up the majority of cases in the current Mpox outbreak. We aimed to investigate the perception of and vaccine readiness towards Mpox among MSM living with HIV in China. Methods: This cross-sectional online study was conducted from 10 August to 9 September 2022. Participants responded to survey questions about their socio-demographic information, HIV status, sexual behaviors, knowledge of Mpox, and attitudes towards Mpox vaccines. Results: A total of 577 MSM living with HIV participated in the study. A total of 37.6% expressed concerns about the Mpox epidemic in China, and 56.8% were willing to get the Mpox vaccine. Men who had > four sexual partners in the previous three months (aOR = 1.9 95% CI: 1.2–2.8 Ref: 0), had close contact with > four individuals in a day (3.1, 1.5–6.5 Ref: 0–3), were worried about the Mpox epidemic in China (1.6, 1.1–2.3 Ref: No), and believed that Mpox vaccines are safe (6.6, 2.7–16.4 Ref: No or not sure) and effective (1.9, 1.1–3.3 Ref: No) for people living with HIV were more likely to be willing to get the Mpox vaccine. MSM living with HIV with a high school education or below (0.5, 0.3–0.9 Ref: Postgraduate diploma), and sometimes (0.5, 0.3–0.8 Ref: Often), seldom, or never (0.5, 0.3–0.9 Ref: Often) followed news about Mpox were unwilling to get the Mpox vaccine. Conclusion: The ongoing Mpox pandemic has not attracted widespread concerns among MSM living with HIV in China. Having more sexual partners and close contacts, worrying about the Mpox epidemic, and believing in the vaccine’s safety and efficacy were predictors of their willingness to get the Mpox vaccine. Efforts should be made to raise awareness of the potential risk of Mpox in this at-risk population. Public health strategies should fully address predictors of vaccination willingness.