Online courses play an increasing role in professional development of environmental educators, yet little information is available on the interactive processes involved in online learning. We examined the relationship of three types of interactions in an urban environmental education online course--participant-participant, participant-instructor, and participant-content--to four course outcomes: participants' motivation to learn, intent to adapt ideas and information learned through the course in their practice, actual adaptation of ideas in their practice, and development of professional networks. Content analysis was used to characterize participants' and instructors' weekly online posts and comments, and generalized estimation equation modeling was used to explore the relationships between interactions and outcomes. The results showed that participant-content interaction had significant positive relationships with participants' motivation to learn, intent to adapt ideas, and adaptation of ideas. Participant-participant interaction had significant positive relationships with participants' motivation to learn, and development of professional networks with each other. Finally, participant-instructor interaction had a significant positive relationship with participants' development of professional networks. The results of this study can be used to improve professional development online courses for environmental educators.