The purpose of this study was to examine the effects of the type of exploratory strategy and level of prior knowledge on middle school students' performance and motivation in learning chemical formulas via a 3D role-playing game (RPG). Two types of exploratory strategies-RPG exploratory with worked-example and RPG exploratory without worked-example--and two levels of prior knowledge--high prior knowledge and low prior knowledge-were examined in the study. The "5E Instructional Model" was employed as a learning framework in the RPG game design of "The Alchemist's Fort." One hundred and fifteen eighth-grade students from a Taiwanese school voluntarily participated in the 3-week experiment. The results indicate that (1) significant worked-example effect was revealed on knowledge comprehension and marginal worked-example effect occurred on knowledge application; (2) regardless of the type of exploratory strategy employed, learners showed mild positive motivation toward learning chemistry via a 3D RPG game; (3) higher prior-knowledge learners outperformed their lower prior-knowledge peers on performance measures; and (4) high prior-knowledge learners showed a higher degree of motivation in self-efficacy and science learning value than did the low prior-knowledge learners; however, lower prior-knowledge learners revealed higher learning environment stimulation than did their high prior-knowledge peers.