This study aimed to investigate the relationship among quadriceps femoris muscle architecture, jump performance, and age in months in junior high school basketball players. Nineteen male junior high school basketball players (age, 13.7±0.7 years［168.1±9.5 months］；height, 166.3±10.3 cm；body mass, 54.3±12.6 kg；competitive career duration, 5.3±1.7 years) volunteered to participate in this study. We measured the vertical jump (VJ) and running jump heights using a single leg (RJS) or both legs (RJB). Quadriceps femoris (vastus medialis oblique［VMO］, vastus medialis［VM］, rectus femoris［RF］, vastus intermedius［VI］, vastus lateralis［VL］) muscle thickness (MT) was measured using real-time ultrasonography. The total MT of the VMO, VM, RF, VI, and VL was calculated (Total). Pennation angle (PA) was measured at the RF and VL. Images were analyzed by an image analysis software and fascicle length (FL) of the RF and VL were calculated by MT and PA. The ratio of MT to body mass1/3（MT/BM1/ 3 ratio) was calculated to normalize the morphological differences. We observed a significant correlation between VJ and MT of the VMO (r＝0.558, p＝0.013), RJB and MT of the VMO, RF, Total (VMO, r＝0.538, p＝0.017；RF, r＝0.483, p＝0.036；Total, r＝0.539 p＝0.017), and between RJS and MT of the VL (r＝0.536, p＝0.018). We also observed a significant correlation between RJB and FL in VL (r＝0.569, p＝0.011). There were significant correlations between MT and MT/BM1/ 3 ratio in VMO and age in months (MT, r＝0.659, p＝0.002；MT/BM1/ 3 ratio, r＝0.511, p＝0.026). The results of the present study suggest that different parts of the quadriceps femoris muscle are related to jump performance in junior high school basketball players. When growth spurts occur during the age of junior high school student (12-15years old), VMO distal to the VM may increase specifically.