The objective of this research aimed to determine and analyze the relationship between Social Media Marketing, Customer Retention, and Customer engagement as a Mediating Variable for Shopee e-commerce users in Palembang City. The research design uses a quantitative approach with 130 respondents. The types of data used in this study are primary and secondary data. Primary data was obtained from questionnaire results, and secondary data was obtained from literature such as books and journals. The data analysis technique used is SEM analysis with the PLS 3.0 program. The results of this study indicate that Social Media Marketing has a positive effect on Customer Retention and Engagement, Customer Retention has a positive effect on Customer Engagement and Customer engagement successfully mediates the relationship between Social Media Marketing and Customer Retention. This research is expected to be useful for e-commerce Shopee and others, to increase Customer Retention and strengthen Customer Engagement.