The field of online professional development is in ongoing growth, and motivation has been identified as a critical factor in online courses. Somewhat different from the common courses delivered through MOOCs, this study investigates learning processes in compulsory courses. The study aims to understand the motivational factors influential on the behaviors of faculty members in a compulsory professional development program. The participants included 11 instructors who completed the program. Within the lens of self-determination theory, the motivation of instructors was determined through semi-structured interviews, which were analyzed through content analysis. Prominent factors affecting motivation were found as (a) the nature of professional development, (b) teaching materials, (c) evaluation, (d) learning environment, and (e) external factors (compulsory participation, environmental pressure). Attending a compulsory course is discussed in terms of self-determination theory. The implications of notable findings and directions for future studies are also discussed.