Improving men's engagement in HIV prevention is not only essential for reducing their own HIV risk but also the risk of transmitting HIV to their female partners. We conducted a cross-sectional survey using a population-based sample of men (age 18-30) who reported being a partner of an adolescent girls and young women (AGYW) in South Africa (N = 2827). We used logit-binomial regression models to examine associations among men's partnership characteristics, HIV risk perceptions, and HIV-related behaviors and examine differences by male partner age (younger men (18-24) vs. older men (25-30)) and age difference between partners (age-concordant (< 5 years) vs. age-disparate (≥ 5 years)). Most men reported inconsistent condom use (85%) and nearly half reported engaging in transactional sex (48%). Older men were just as likely as younger men, and men with age-disparate and age-concordant partners, to inconsistently use condoms, engage in transactional sex, and perpetrate intimate partner violence. Most men also reported a very high interest in pre-exposure prophylaxis (PrEP) (77%) and half reported having an HIV test in the past year (50%). There were no differences by male partner age or age difference between partners in PrEP interest but older men and men in age-discordant relationships were more likely than younger men and men in age-concordant relationships to have an HIV test in the past year. Male partners of AGYW in South Africa are engaging in HIV-related behaviors and need HIV prevention interventions to reduce risk for themselves and their female partners.