This research was conducted at PT. Mega Prakarsa Engineering Indonesia involving 153 respondents as customer representatives. The purpose of this study was to determine the role of mediation of customer satisfaction on the influence of service quality and social media marketing on customer loyalty. The results showed that service quality has a significant effect on customer satisfaction. Social media marketing has a significant effect on customer satisfaction. Service quality has a significant effect on customer loyalty. Social media marketing has a significant effect on customer loyalty. Customer satisfaction has a significant effect on customer loyalty. Service quality has a significant effect on customer loyalty through customer satisfaction. Social media marketing has a significant effect on customer loyalty through customer satisfaction.