[Purpose] The purpose of this study was to investigate the changes of muscle activity during squat motion after stretching the tensor fasciae latae muscle. [Participants and Methods] The participants comprised 19 healthy males. The test muscles were the vastus medialis obliquus and vastus lateralis. The participants performed the squat motion before and after stretching the tensor fasciae latae. We measured the muscle activities and the onset timing of the vastus medialis obliquus relative to that of the vastus lateralis during squat motions. [Results] The onset timing of the vastus medialis obliquus relative to that of the vastus lateralis was decreased, and the vastus medialis obliquus activity and vastus medialis obliquus/vastus lateralis activity ratio were increased after stretching the tensor fasciae latae. [Conclusion] This study revealed that stretching of the tensor fasciae latae increases the relative vastus medialis obliquus muscle activity.