The fringe-field switching (FFS) mode has unique characteristics such as high transmittance and wide viewing angle and its electro-optic characteristics strongly depend on pixel electrode width (w) and distance (l) between them. In this study, optimal phase retardation of the FFS mode using a liquid crystal (LC) with negative dielectric anisotropy depending on pixel electrode structure was investigated based on the simulation. The results shows that when the width of the pixel electrode and distance between electrodes are 3 mu m and 4.5 mu m, respectively, the cell shows transmittance 0.87 with optimal phase retardation value of LC cell 0.36 mu. As w and l are decreased to 1 mu and 1.5 mu, the cell shows transmittance of 0.90 with optimal phase retardation of LC cell 0.40 mu, indicating that the light modulation method is changed according to electrode structure.