The foot sole of the biped robot is an important factor for stable walking. In this study, the limitations of existing bipedal robot soles are introduced and the necessity for the development of a new sole mechanism is presented. Inspired by a robot sole based on the granular jamming effect, we have developed a variable stiffness sole (VSS), which adapts to the shape of obstacles on the ground in compliant mode and provides robust support in stiff mode. Finally, the performance of the VSS is verified by several experiments integrating the VSS with the real humanoid robot platform RoK-3. The experimental results verified that the VSS is advantageous in uneven terrain walking.