Graft copolymers of high density polyethylene(HDPE) and acrylic acid(AA) were prepared by the photoinduced grafting technique. The properties of HDPE-g-AA copolymer films of different graft yield were evaluated. Measurement included gel percent, thermal property, mechanical property, and change of morphology. The insoluble part of the grafted film after extraction with p-xylene and methanol was increased as increasing the graft yield. Results of thermal property indicate that the grafting occurred in the amorphous region without disrupting the crystalline part of HDPE film. As the graft yield was increased, the initial modulus and tensile strength at yield point were increased but the elongation was decreased.