The bipedal humanoid robot WABIAN-2R is developed to simulate human locomotion. Performing a walking motion requires a high torque at the ankle joint. WABIAN-2R consists of harmonic gears in its driveline system which increases the weight of each leg and respectively decreases the energy economy. Therefore, a new idea is proposed and developed in this paper through computer simulation to modify the design of the ankle joint by adding a spring mechanism instead of high gear ratio transmission. This helps reduce the energy consumed while walking; by storing and returning part of the energy. Research presented in this paper proposes an important step toward developing the passive dynamics walking into the advanced complex humanoid robots.