This paper presents a Lyapunov-based positioning controller for a macro-micro arm suppressing the bending vibration of the macro arm. On the basis of the distributed parameter model, the output feedback control law is constructed using Lyapunov method. The asymptotic stability on the neighborhood of the desired states of the closed-loop system is proved. The proposed controller consists of the PD feedback of the motor angle and a feedback of the bending strain at the tip of the macro arm. Some simulations are performed to show the effectiveness of the proposed controller.