Many of the characteristics and nature of teaching massive open online courses (MOOCs) are different from face-to-face teaching, which can directly affect instructors' work engagement and ultimately the success of MOOCs. As such, this study investigated the effects of openness, altruism and instructional self-efficacy on MOOC instructors' work engagement. A total of 209 MOOC instructors participated in an online survey, and their responses were analyzed. The research findings indicated that openness to experience influenced MOOC instructors' instructional self-efficacy and work engagement. Altruism did not directly influence work engagement of MOOC instructors; however, it indirectly affected work engagement through instructional self-efficacy. Instructional self-efficacy also affected MOOC instructors' work engagement and fully mediated the relationship between altruism and work engagement. The variables examined in this study, openness, altruism and instructional self-efficacy, were found to significantly influence work engagement of MOOC instructors. As the number of MOOCs and MOOC students increase, the importance of MOOC instructors and their work engagement will be crucial for the success of these courses. Thus, additional research is needed on the ways to enhance MOOC instructors' work engagement.