On the basis of stimulus-organism-response (SOR) theory, this study extends the work of Lee and Kwon by examining the concept of perceived usefulness as a mediator between emotional interaction (familiarity and intimacy) and purchase intention. The consumer purchase decision model, in which product type plays a moderating role in the linking mechanism, is also explored.We proposed a consumer purchase decision model, and empirically examined it by means of an online questionnaire survey. Confirmatory factor analysis and structural equation modeling with bootstrapping estimation were conducted using the data obtained from 269 social commerce users.Familiarity and intimacy positively affected the users' purchase intention in social commerce. Perceived usefulness mediated the relationship between emotional interaction and purchase intention. Moreover, product type moderated the following relationships: between familiarity and purchase intention, between intimacy and purchase intention, and between perceived usefulness and purchase intention.The results support this study's hypotheses and SOR theory. Purchase intention could be enhanced by improving emotional interaction and perceived usefulness.