This study examines the relationship between social media marketing and brand loyalty through brand trust. Respondents were drawn from customers of McDonald’s, Malang City, East Java Province, Indonesia. For this study, 130 questionnaires were distributed and data were analyzed using the Structure Equation Model (SEM) version 22 of the AMOS (Analysis of Moment Structure) application. The results showed that social media marketing had an impact on increasing McDonald’s brand trust and brand loyalty. Brand trust influences brand loyalty and brand trust can mediate the influence of social media marketing on McDonald’s brand loyalty. The findings prove that brand trust can mediate the effect of social media marketing on customer loyalty to McDonald’s brand. These results can be explained by the fact that marketing strategies through social media marketing, such as making it easy for customers to get information related to McDonald’s on social media, can contribute to customer trust and that trust is formed because McDonald’s always pays attention to the quality of the products offered. Brand trust can mediate the influence of social media marketing on customer loyalty to McDonald’s brand. This means that information related to McDonald’s on social media is proportional to the quality of the product offered.