This study aims to examine a moderated mediation model wherein core self-evaluation (CSE) and horizontal collectivism (HC) interact to predict negative emotional reactivity to interpersonal conflict, and thus HC moderates the indirect effects of CSE on subjective well-being (SWB) through emotional reactivity. A short-term prospective study was conducted with 257 South Korean university students. Participants completed measures of CSE and HC, and then reported their experiences with interpersonal conflict and SWB in an online survey about two weeks later. We found that, among low HC participants, after controlling for the importance of conflict issues, individual differences in CSE predicted emotional reactivity to interpersonal conflict, and emotional reactivity was in turn negatively associated with SWB. By contrast, among high-HC participants, emotional reactivity to interpersonal conflict did not differ as a function of CSE, and the indirect effects of CSE on SWB were not significant. These findings highlight the importance of high CSE and HC values in fostering emerging adults’ resilience against the detrimental effects of interpersonal conflict in sustaining individuals’ SWB. Implications for conflict management interventions are discussed.