Teachers recognize the importance of professional development (PD) but often struggle with low motivation and provide negative feedback. While studies highlight the need for teacher PD, there is insufficient discussion on what makes PD engaging. In this paper, we present a design case of a motivationally enhanced asynchronous PD session for in-service teachers using the ARCS motivational design model. To illustrate the motivational design process of a PD program for in-service teachers, we discussed examples of motivational interventions and strategies. Then we showcased the ARCS-based motivational design process using the 10 steps of systematic design approach. The design case will be beneficial for instructional designers who are involved in creating an engaging PD for teachers.