Self-directed learning (SDL) is a critical success factor for massive open online course (MOOC) learners. This meta-analysis study examined the influence of SDL on learning outcomes in MOOCs by extracting the effect sizes of 60 samples from 14 studies published between January 2010 and April 2022. The results showed that the overall effects of SDL on learning outcomes in MOOCs have a medium effect size, which supports many previous studies that have reported positive effects of SDL on academic achievement in MOOCs. There was also a significant difference in the effect size of SDL on learning outcomes among adult learners, undergraduates, and middle and high school students. The influence of self-management on learning outcomes was significantly smaller than on motivation and self-monitoring. However, there were no significant differences in affective, cognitive, and behavioral learning domains in terms of the influence of SDL on learning outcomes.