Previous research has emphasized the important role of interest in education. However, only a few studies have investigated situational interest in game-based learning environments. Therefore, this study aims to clarify the role of situational interest in game-based mathematics learning by examining its relations with learning outcomes, self-efficacy, and math interest. Ninety-eight 7th-grade participants played the Number Trace rational number learning game for three 45-minute lessons. Pre-and post-tests were used to measure rational number conceptual knowledge and self-reported measures of math interest. Situational interest and selfefficacy were measured within the game environment. Results indicated that situational interest and learning outcomes were positively related. Furthermore, self-efficacy, as well as math interest, were positively related to situational interest.