An optimal condition to modify poly(dimethylsiloxane) (PDMS) surface for microchannel electrophoresis in a quick and simple manner was investigated. PDMS has the native hydrophobicity property and negative charge on its surface. These disadvantages limit the use of PDMS in electrophoresis application, because they cause bio-fouling and electroosmotic flow (EOF). One of the promising approach is surface modification by biocompatible polymer. 2-Methacryloyloxyethyl phosphorylcholine(MPC), which has suitable property of protein adsorption resistance, was graft polymerized from the PDMS surface using UV irradiation. Optimization of the surface modification was performed by graft polymerizing with various concentration of the monomer concentration and UV-irradiation time. The resulting surfaces were characterized by X-ray photoelectron spectroscopy (XPS), surface zeta potential, and protein adsorption test. The polymerizing condition is believed to intercorrelate with graft density of MPC polymer. The high graft density of MPC polymer on PDMS can suppress both non-specific protein adsorption and EOF.