<p>Maintaining and improving the work ability and motivation of older workers is considered successful aging at work. Unfortunately, existing research on the antecedents of successful aging at work, especially in terms of interpersonal interactions, remains insufficient. Drawing on conservation of resource theory, we constructed a moderated mediation model in which workplace interpersonal capitalization affects successful aging at work via harmonious passion, with coworker responsiveness as a second-stage moderator. To test our model, we conducted a three-wave survey to collect data from 365 employees, aged 45 to 55, in China. The results displayed that workplace interpersonal capitalization was positively related to successful aging at work and harmonious passion mediated this relationship. We also found that coworker responsiveness reinforced the positive relationship between harmonious passion and successful aging at work. Our study enriches the investigation into the antecedents of successful aging at work through the lens of interpersonal interactions. In the era of extended working lifespans and delayed retirement ages, our research offers organizational managers and practitioners new perspectives on successful aging at work from the viewpoint of interpersonal interactions.</p>