Social TV, a new interactive television service, has been rapidly developing. With the conceptual model of sociability, this study empirically investigates the effects of perceived sociability on the motivations and attitudes toward Social TV. A model is created to validate the relationship of perceived sociality to social presence, usability, and intention. Empirical findings show the key influence of sociability on users' acceptance and intent to continue using Social TV. Implications of the findings are discussed in terms of building a theory of sociability and providing practical insights into developing a meaningful sociable TV interface.