Game-based learning is supposed to motivate learners. However, to what degree does motivation driven by interest in playing an instructional game affect learning outcomes compared to motivation driven by interest in the very learning process? This is not known. In this study with a unique design and intervention, young adults (N = 128; a heterogeneous sample) learned how to control an electro-mechanical device in a 40minute-long learning session integrated into a 2-hour-long educational live action roleplaying game (edu-LARP). Edu-LARPs are supposedly engaging games where players take part in team role-playing by physically enacting characters in a fictional universe. In our edu-LARP, players had to understand how the to-be-learned device worked in order to win the game. Departing from typical game-based learning research, learningand playing-related variables were assessed for each learner separately (i.e., a withinsubject design). Affective-motivational factors related to playing (rather than learning) predicted learning outcomes in a positive, but considerably weaker, way compared to learning-related, affective-motivational factors. Developed interest in LARP-like games was primarily related to enjoying the game rather than better learning outcomes; whereas, developed interest in the instructional domain was primarily related to enjoyment of learning and better learning outcomes. Overall, autonomous motivation to play was connected to higher learning outcomes, but this connection was weak.