This paper proposes the use of disturbance observer-based control (DOBC) for the output voltage regulation in DC-DC boost converter. The proposed controller consists of combining linearizing feedback control with disturbance observer. Specifically, the feedback controller is designed considering the nominal model with a view to ensure closed-loop stability, while the disturbance observer is employed to compensate for model uncertainties and unknown disturbances. Thus, zero steady-state error is guaranteed under the composite controller. The asymptotic regulation is achieved due to the integral action property characterizing the disturbance observer. However, the integral action can deteriorate the transient response during control saturation, even destroy the closed-loop stability, due to the integrator build-up. This problem is solved in this paper by considering control saturation in the observer design. After mathematical manipulation, it turns out that the composite controller reduces to a dynamic state feedback control plus an anti-windup scheme to mitigate the effect of control saturation during transients. The performance of the proposed controller was verified by simulation tests. The simulation results demonstrated the ability of the proposed controller to achieve good transient and steady-state performances.