This study investigates the effects of students’ intrinsic motivation and prior knowledge on student achievement in learning Chinese in a game-based learning environment. A total of 140 fourth-grade students from an elementary school in South Korea participated in this study. An instructional game called “Hanjamaru,” which is designed to teach Chinese characters, was implemented for four weeks. During the experiment, students’ prior knowledge, intrinsic motivation in gaming, and achievements learning Chinese were quantitatively measured. Findings from this study demonstrate that both students’ prior knowledge and intrinsic motivation affect their achievements in learning Chinese. Also, there students’ prior knowledge and intrinsic motivation affected each other; that is, a group low in intrinsic motivation but with higher prior knowledge showed comparatively higher student achievements. These findings suggest that students’ prior knowledge should also be considered while designing and adopting game-based learning in order to engage students with different levels of intrinsic motivation.