Cu thin films have been deposited on Si (100) substrate by using a non-mass separated ion beam deposition system. The effect of the substrate bias voltage on the properties of the deposited films was investigated using X-ray diffraction, resistivity measurement and scanning electron microscopy. In the case of Cu thin films deposited without bias voltage, a columnar structure and small grains were observed distinctly, and the electrical resistivity of the deposited Cu films was very high. By applying the substrate bias voltage, no clear columnar structure and grain boundary were observed. The resistivity of Cu films decreased remarkably and reached a minimum value of 1.8±0.1μΩcm at a bias voltage of -50V, which is close to that of Cu bulk (1.67 μΩcm).