Online group buying (OGB) has recently captured the attention of academic researchers. Because of the lack of an integrated perspective of external variables in the technology acceptance model (TAM), we investigated the influence of consumer characteristics (economic shopping orientation and prior buying frequency), social influence factors (subjective norms and visibility), and system factors (system quality and information quality) on perceived usefulness (PU) and perceived ease of use (PEOU) of the OGB web site. We also examined the effects of PU and PEOU on attitudes and behavioral intention. We collected 1,163 useable questionnaires through a quantitative online survey, and used structural equation modeling (SEM) to analyze the data. The results show that, whereas economic shopping orientation, subjective norms, and information quality had a positive effect on PU, purchasing frequency and system quality affect the PEOU of the OGB web site. However, the relationship between visibility and PU was non-significant. We integrated consumer characteristics, social influence, and system factors in OGB research, and the findings can assist OGB administrators to improve their understanding of the attendant factors of PU and PEOU to form positive user attitudes toward OGB and increase their reuse and repurchasing intentions.