A method of manufacturing an array substrate for a liquid crystal display device includes forming gate and data lines crossing each other on a substrate; forming a thin film transistor connected to the gate and data lines; forming a passivation layer on the substrate having the gate lines, data lines and the thin film transistor; forming a first conductive material layer on the passivation layer and connected to a drain electrode of the thin film transistor; oxidizing a surface of the first conductive material layer; forming a second conductive material layer on the oxidized first conductive material layer; forming a photoresist pattern on the second conductive material layer; etching the first and second conductive material layers using the photoresist pattern to form pixel and common electrodes which are alternately arranged in the pixel region and produces an in-plane electric field; and removing the photoresist pattern.