Being efficient learners is important in the modern workforce, but improved performance and cognitive load do not imply that students are efficient learners. This study investigated the effectiveness of a personalized role-playing game in students' learning efficiency (LE) and mental efficiency. Results showed that students in the personalized game environment significantly improved LE and mental efficiency compared to the conventional online learning environment. Students were able to achieve higher performance while spending less time and mental effort. Moderate negative relationship was found between performance and mental effort while a strong negative relationship was found between performance and learning time. Learning time might be an indicator of efficient learners when performance is expected at a certain level. This study demonstrated that the personalized game might be an alternative approach to train efficient learners particularly when training time is limited and support complex task training that demands high cognitive investment.