The purpose of this study was to identify the existing level of self-regulated learning (SRL) among Thai online learners, to examine the relationship between SRL and academic achievement based on a) course completion and b) course grades, and to investigate differences in SRL as they correlate to demographic factors. A mixed-methods research design with modified MSLQ online surveys and semi-structured interviews was used during the process of data collection. One hundred eighty-eight of the 580 online learners enrolled in the certificate programs of the Thailand Cyber University Project responded to the surveys; 7 of these also participated in the interview process. The findings indicated that Thai online learners reported high levels of SRL characteristics. Independent sample t-test results revealed that successful learners were higher in SRL learning strategies than those who did not succeed the course. Results from multiple regression analyses indicated that critical thinking and time/study environmental management were significant predictors of academic course grade with a small effect size (R2 = .113). Comparison of mean differences revealed that some SRL characteristics were different among demographic subgroups determined by factors including gender, age range, marital status, and Internet use; female reported a significantly higher level of task value than male; younger learners had a significantly higher level of test anxiety than older learners; married learners reported a significantly higher level of self-efficacy and task value than single learners; online learners who had more Internet experience reported a significantly higher level of self-efficacy, metacognitive self-regulation, and time/study environmental management than those who had less Internet experience. In addition, the qualitative findings confirmed that participants reported the use of learning strategies in four categories, with a high number of references to metacognitive self-regulation and elaboration, and a low number of references to critical thinking and time/study environmental management. Furthermore, the qualitative results revealed that Thai online learners used different tools for social and personal activities, communication, and information searching.