A simple quadrilateral 12 DOF plate bending element based on Reissner-Mindlin theory for analysis of thick and thin plates is presented in this paper. This element is constructed by the following procedure: the variation functions of the rotation and shear strain along each side of the element are determined using Timoshenko's beam theory; andthe rotation, curvature and shear strain fields in the domain of the element are then determined using the technique of improved interpolation.The proposed element, denoted by ARS-Q12, is robust and free of shear locking and, thus, it can be employed to analyze very thin plate. Numerical examples show that the proposed element is a high performance element for thick and thin plates.