Study aim: The purpose of this study was to determine if high school physical education seniors’ health-related fitness knowledge is related to their aerobic capacity and body composition. Material and methods: The FitSmart test assessed students (n = 171) health-related fitness knowledge. Aerobic capacity was calculated based on the students PACER score. Body Composition was measured using the Tanita TBF 300A body composition analyzer. Results: Aerobic fitness was a statistically significant predictor of exam score (β = 0.563, p < 0.001), but percent body fat was not (β = 0.185, p =0.074). Comparing the health-related fitness exam scores by the FITNESSGRAM classification system, students who were classified as Very Lean and High Risk for body composition had lower exam scores than those classified in the healthy fitness zone. Conclusions: The results confirmed previous findings that students have inadequate health-related fitness knowledge. Furthermore, the study extends these findings by identifying some associations of percent body fat and estimated VO2max to health-related fitness knowledge.