Objectives <p>As the population progressively ages, it has become increasingly important to maintain intrinsic capacity (IC) in advanced middle age. Our study aimed to examine gender-specific differences in the reciprocal relationship between IC and social activity among advanced middle-aged adults in South Korea.</p> Methods <p>We used data from the 2016 and 2018 waves of KLoSA, including participants aged 55 to 64 years at baseline (<i>N</i> = 2,273). We measured IC across five domains, and social activity by the total number of social group participation. Cross-lagged panel models were applied with gender-stratified analysis.</p> Results <p>We observed a reciprocal association between IC and social activity, with deteriorating IC at baseline associated with low social activity at follow-up (<i>β</i> = − 0.08, <i>p</i> = .002), and enhanced social activity at baseline associated with subsequently improved IC (<i>β</i> = − 0.03, <i>p</i> = .013). In gender-stratified analyses, worsening IC was significantly associated with subsequently low social activity in males (<i>β</i> = − 0.13, <i>p</i> = .006). Enhanced social activity was significantly associated with correspondingly improved IC in females (<i>β</i> = − 0.04, <i>p</i> = .022).</p> Conclusions <p>Our study highlights gender-specific patterns in the reciprocal relationship of IC with social activity in advanced middle age. Optimum IC could be prioritized with interventions in working males, whereas sustained social participation might be facilitated by strategies in females. Early, gender-specific approaches in advanced middle age may contribute to healthy, ageing trajectories.</p>