This instrumental case study explored 10 English as a foreign language (EFL) instructors' perceptions and experiences of participating in an asynchronous online professional development (OPD) program. The study aimed to explore instructors' professional development (PD) needs, the factors influencing their participation in OPD, and the perceived effective characteristics of the OPD program. Data gathered through individual interviews, reflective reports, and a focus group were analyzed using a reflective thematic analysis approach. The study revealed that the EFL instructors' limited engagement in reflective practice and continuous PD could potentially result in overconfidence and a lack of awareness regarding their PD needs. Furthermore, the article highlights perceived effective characteristics of the OPD program: flexibility, collaboration, facilitation and organization, reflection, relevance, and practicality. Findings suggest that these characteristics not only contributed to its effectiveness but also promoted instructors' participation and engagement in the OPD.