This paper presents an improved equivalent-inputdisturbance (IEID) approach for disturbance rejection. It can be used for both minimumand nonminimum-phase plants. First, a full-order generalized state observer (GSO) is employed in the construction of an IEID-based servo system to estimate an equivalent input disturbance. Then, a stability condition is derived and a GSO design algorithm is developed based on the stability condition and a pole placement algorithm. Finally, a numerical example demonstrates the validity of this method.