Online courses have been criticized for their focus on knowledge acquisition rather than on how to solve authentic complex problems, a skill that is increasingly being recognized as critical to meeting the challenges in the real world. The purpose of this study was to explore whether between-group collaboration in project-based online courses can promote student learning of complex problem solving. Eleven graduate students in an educational technology class participated in this study. Each group of three to four members designed and developed a 2-week online mini-course that was later implemented with classmates across groups. During the semester, students were encouraged to visit other group areas, discuss challenges, and share strategies in the online course environment. The results indicate that between-group collaboration was effective in improving group processes, group project performance, individual student achievement, and confidence in complex problem solving in designing online courses.