Blends were prepared from high density polyethylene(HDPE) and thermoplastic starch(TPS). Mechanical properties, thermal properties, and morphology were investigated and also biodegradability was studied by using aerobic composting method (ISO14855). Tensile strength, modulus and elongation at break decreased as the content of TPS increased. Especially, elongation rapidly decreased even at the lower content of TPS. The glass transition temperatures of blends were not changed. Biodegradability of blends increased as the content of TPS increased. The morphology of the fractured surface of blend film was investigated by scanning electron microscophy(SEM).