Introduction Profound sexual health disparities exist for Black men who have sex with men (MSM) in the US South, including high prevalence of sexually transmitted infections (STIs). STI prevention strategies beyond condoms are needed for Black MSM taking PrEP. Methods We conducted in-depth interviews with Black MSM taking PrEP. Informed by the Health Belief Model, we asked about participants’ STI knowledge; perceived susceptibility, severity, and concerns; and perceived benefits of STI prevention. We also asked about support systems, condom use norms, and various STI prevention strategies, particularly peer support via an mHealth application. Interviews were audio-recorded and analyzed using directed content analysis. Results We interviewed 20 Black MSM ages 18–35. Eight had an STI diagnosis within 12 months; most (n=15) had been taking PrEP for more than one year; 15 identified as gay, 4 as bisexual, and 1 as queer; and 17 had insurance. Participants felt well-informed about STI symptoms, transmission, and treatment. Most had concern about an STI diagnosis, noting shame or disappointment. Potential long-term effects were described as concerning but not frequently considered. Almost all reported strong social support from family or friends. Participants described being less likely to use condoms with routine partners or those on PrEP, noting the norm ‘had switched from condoms to PrEP.’ Most were willing to test for STIs more frequently (e.g. monthly), but desired convenience. Most said they would deliver partner therapy and some desired STI education. Although some did not use social media, most felt app-based social support would be helpful. Conclusion Black MSM on PrEP voiced concern about STIs but many noted condom use was no longer the norm. They were willing to engage in methods focused on preventing STIs on an individual- or population-level. Most had sources of social support but still desired app-based peer support from other MSM.