Poly(glycidyl methacrylate)-grafted polyethylene microbeads (PGPM) presenting epoxy groups were prepared by radiation-induced graft polymerization of glycidyl methacrylate on the polyethylene microbead. The obtained PGPM was characterized by IR spectroscopic, X-ray photoelectrons spectroscopy (XPS), scanning electron microscope (SEM), and thermal analyses. Furthermore, the abundance of epoxy groups on the PGPM was determined by titration and elemental analysis after amination. The epoxy group content was calculated to be in the range 0.29~0.34 mmol/g when using the titration method, but in the range 0.53~0.59 mmol/g when using elemental analysis (EA) after amination. The lipase was immobilized to the epoxy groups of the PGPM under various experimental conditions, including changes to the pH and the epoxy group content. The activity of the lipase-immobilized PGPM was in the range from 160 to 500 unit/mg·min. The activity of the lipase-immobilized PGPM increased upon increasing the epoxy group content. The lipase-immobilized PGPM was characterized additionally by SEM, electron spectroscopy for chemical analysis (ESCA), and EA.