<p>Purpose: The purpose of this study was to validate for leg and vertical stiffness estimated by using Morin's method. </p><p>Method: One hundred twenty seven children participated in this study. Each subject sprinted for 50 m. The motion through an interval from 30 m to 40 m was recorded with high-speed camera at 300 Hz from the sagittal plane. The running speed, contact time in stance phase and flight time were measured to estimate maximal force exerted on the foot (F_max), vertical stiffness (k'_vert) and leg stiffness (k'_leg) by Morin's method (2005). In gold standard method (MacMahon and Cheng, 1990), vertical excursion of center of mass and leg spring length variation was calculated from digitized landmarks and ratios of F_max to vertical excursion of center of mass and to leg spring length variation were calculated as the vertical stiffness (k_vert) and leg stiffness (k_leg). </p><p>Result: All values are represented in mean value±standard deviation (SD). k'_vert was 15.51±5.97 kN/m, whereas k_vert was 17.92±6.59 kN/m. The mean difference of the k'_vert between k_vert was -2.41±2.62 kN/m. ICC between k'_vert and k_vert was 0.851 (p<0.001). Mean k'_leg and k_leg was 5.21±1.91 kN/m and 6.81±2.57 kN/m. ICC between k'_leg and k_leg was 0.642 (p<0.001), while k'_leg was highly correlated with k_leg (r=0.839). Additionally k'_leg was underestimated (-23.6%) to k_leg.</p><p>Conclusion: We could conclude that Morin's method might be able to estimate vertical stiffness and leg stiffness in children, although vertical and leg stiffness tended to be underestimated.</p>