This study examines the predictive utility of students' motivation (self-efficacy and task values) to their physical activity levels and health-related physical fitness (cardiovascular fitness and muscular strength/endurance) in middle school fitness activity classes. Participants (N = 305) responded to questionnaires assessing their self-efficacy and task values (perceptions of importance, interest, and usefulness) toward fitness activities near the end of the school year. They completed the PACER and curl-up tests to measure their cardiovascular fitness and muscular strength/endurance, respectively. Then their physical activity levels in one fitness class were measured via pedometers during a 1-week follow-up. Regression analyses suggested that students' self-efficacy, perceptions of importance, interest, and usefulness of fitness made significant contributions to the prediction of their physical activity levels in class. Self-efficacy was the only significant predictor of cardiovascular fitness, whereas none of the motivational variables emerged as predictor of muscular strength/endurance. The educational implications are provided for teachers and health professionals. (Contains 2 tables.)