Recent empirical research indicates the amount of time children between 9-17 years of age with autism spectrum disorder (ASD) spend in physical activity is lower than typically developing peers and sadly declines as children become older. The purpose of this study was to examine the relationship between components of health-related physical fitness (i.e., aerobic capacity and muscular strength) and school-day physical activity behavior of children with ASD (9-17 years). School-day physical activity was measured using the Omron HJ-720ITC pocket pedometer. Health-related physical fitness components aerobic capacity was measured using the six-minute walk test, while muscular strength was measured using handgrip strength. Results indicated a significant relationship between aerobic capacity and the steps accumulated during school ( B = 0.336, p = 0.02 ). This study provides an initial step in identifying key determinants of physical activity of children (i.e., 9-17 years of age) with ASD. Subscribe to PALAESTRA