In this paper, a method of optimizing the rolling amplitude needed for a stable and smooth walking movement of a humanoid robot is considered. The optimization algorithm was based on minimizing a cost function defined by the rolling overshoot. The amplitude of the rolling during locomotion was calculated using the lateral zero moment point (ZMP) position. The initial value of the rolling was the static rolling that corresponds to the position of the ZMP at the center of the support polygon. The algorithm consisted of performing a ZMP calculation at two points that correspond to single support phases. Simplifying the robot as an inverted pendulum, the gyro feedback controller parameters were tuned to have a passive-like walking motion and a faster response of the robot state to the equilibrium point at single support phase. Experimental results, using HOAP-3 of Fujitsu, showed that the algorithm was successfully implemented along with the locomotion controller. With the optimal rolling technique, the humanoid robot could exhibit a stable and smooth walking movement.