Background: This study examined the association between fitness change and subsequent academic performance in Taiwanese schoolchildren from 7th grade to 9th grade. Methods: The 7th graders from 1 junior high school district participated in this study (N=669). Academic performance was extracted from school records at the end of each grade. Cardiovascular (CV) fitness, sit-and-reach flexibility, bent-leg curl-ups, and height and weight for calculating body mass index (BMI) were assessed at the start of each grade. Results: The results showed that improvement in CV fitness, but not muscular endurance or flexibility, is significantly related to greater academic performance. A weak and nonsignificant academic-BMI relationship was seen. Conclusion: CV fitness exhibits stronger longitudinal associations with academic performance than other forms of fitness or BMI for adolescents. (Contains 3 tables and 1 figure.)