With the advent and popularity of brand communities in digital social networks the communication between companies and people has become faster and more dynamic. Therefore, more and more companies are creating their fanpages on Facebook as a way to be closer to their customers and foster loyalty. The present study intends to investigate how social media-based brand communities affect brand loyalty. Research has been conducted in the existing literature on the subject, indicating that this relationship can be explored through the following constructs: functional benefits, social-psychological benefits, hedonic benefits, community commitment and word-of-mouth. This research tests a model to evaluate the relationships between these constructs in the formation of brand loyalty. Data were collected via an online survey applied to McDonald s community members on Facebook and were analyzed via structural equation modeling (SEM). The results confirmed all but one of the research hypotheses, suggesting that social media-based brand communities can influence in the construction of brand loyalty.