This study aims to investigate the antecedents and consequences of the perceived usefulness (PU) of smoking cessation online health communities (OHCs). In the proposed research model, the informational, emotional, and esteem supports are conceptualized as the antecedents of PU. Two different post-adoption behaviors of users are considered as consequences of PU: (1) continuance intention to use smoking cessation OHCs and (2) knowledge-sharing behavior. We tested the research model by using an online survey of 173 valid responses. The results show that emotional and esteem support are important determinants of PU, and that PU positively affects both knowledge sharing and continuance intention. Continuance intention was found to affect knowledge sharing positively. This study contributes to information systems (IS) post-adoption behavior research in smoking cessation OHCs from the social support perspective and offers practical implications for the administration of smoking cessation OHCs.