The purpose of this study was to examine the effects of instructional approach and prior knowledge on eighth-graders' performance and motivation towards science by implementing 5E learning cycle and 3D immersive RPG. Types of instructional approaches, demonstration and non-demonstration, and prior knowledge were employed in this study. There were 105 eighth-graders participated in this study. The results revealed that: 1. 5E learning cycle with demonstration was helpful to eighth-graders in promoting science learning achievement; 2. students with high prior knowledge achieved better learning performance; and 3. all participants held positive motivation towards using this game-based learning activity for learning science.