In a market with a fierce level of competition, loyal customers are needed to be able to stay competitive. In this era of connectivity, loyalty can be increased through customer engagement on a brand's social media account. Sociolla is a beauty e-commerce platform that uses social media to increase brand loyalty through customer engagement. This study aims to analyze the effect of social media marketing on brand loyalty through customer engagement on Sociolla's Instagram account. The research uses descriptive-causal with a quantitative approach using purposive sampling, given to 100 respondents. This study uses structural equation modeling (SEM). The data was processed using the SmartPLS 3.3 software. The results obtained in this study are social media marketing has a positive and significant effect on customer engagement, customer engagement has a positive and significant effect on brand loyalty, social media marketing has a positive and significant effect on brand loyalty, and social media marketing has an indirect effect on brand loyalty through customer engagement. For this reason, Sociolla should consider improving social media marketing because it will affect customer engagement and brand loyalty. Keywords: e-commerce, social media marketing, customer engagement, brand loyalty.