The present invention relates to a lab-on-chip substrate, comprising a resin having a silicon content of 10% or less by weight as its base material and a hydrophilic polymer covalently bound onto the surface thereof by high-energy ray irradiation, and in particular, to a protein-processing chip. The present invention provides a lab-on-chip substrate resistant to washing and usable for an extended period of time without adsorption of proteins on the base material surface, i.e., a protein electrophoretic polymeric chip having a microchannel allowing high-accuracy analysis of trace amounts of proteins because of reduction in the amount of detection noise.