Problem Statement and Purpose: In Japan, children who exercise and those who do not are increasingly polarized.A child's weight-height ratio varies greatly depending on their exercise habits.This study's main aim is to identify links between body mass index and exercise levels.Thus, we examine the relation between children's Rohrer index and their motor ability demonstrated in physical fitness tests.Approach: The correlation between weight-height ratio (Rohrer index) and motor abilities were investigated using the height, weight, and physical fitness test data of second-and fifth-grade students in Osaka Prefecture in 2017.The physical fitness test measured grip strength, sit-ups, sitting trunk flexion, side step, 20 m shuttle run, 50 m run, standing long jump, and softball throw.A multiple regression analysis between the Rohrer index and each motor skill was conducted, with items showing correlation and significance being analyzed via a quadratic regression curve.Results and Conclusions: Among fifth-grade students, the Rohrer index was correlated with the 50 m run, 20 m shuttle run, and standing long jump (boys: 50 m run R＝0.6986,P < 0.001;20 m shuttle run R＝0.5271,P < 0.001; standing long jump R＝0.5022, P < 0.001; girls: 50 m run R＝0.2200,P < 0.05;20 m shuttle run R＝0.3489,P < 0.01; standing long jump R＝0.4583, P < 0.001).Furthermore, the coefficient for boys was higher than that for girls.No correlation was observed among second-grade students except for boys'20 m shuttle run.In terms of weight-height ratio, a correlation was found betweenacute aerobic exercises (50 m run and standing long jump) and endurance exercises (20 m shuttle run).Children require exercise and physical activity that correspond to their development.