An energy efficient biped robotic system with passive-dynamic locomotion includes a body having a frame. An energy recapture mechanism is suspended within the frame. The energy recapture mechanism includes a load, a mechanical energy storage mechanism that interconnects the load and the frame, and a guide means secured to the load and the frame. A mechanical energy input mechanism interconnects the load with an electric energy generating mechanism. An output means transfers the generated electric energy to an energy storage device. The robot also includes a leg connected to the body portion. The cyclical movement of the leg during passive-dynamic locomotion is transferred to the load through the mechanical energy storage mechanism, and the resulting oscillatory movement of the load is transferred by the mechanical energy input mechanism to the electric energy generating mechanism. The generated electric energy is transferred to the energy storage device for use by the robotic system.