Cu thin films were deposited by bias sputtering and the film density was measured by grazing incidence X-ray reflectivity. The influence of the experimentally measured film density on residual stress and resistivity, which previously few studies reported on, was investigated. Without bias voltage, the relative film density was low and the tensile stress was high. With increasing bias voltage, the tensile stress decreased and saturated to nearly zero at a bias voltage of -100 V, while the film density increased and saturated to nearly bulk value at a bias voltage of -100 V. These results were consistent with those from previously reported molecular dynamic simulations. From the consideration of the Morse potential for relatively dense films, it was possible that tensile stress decreased as the film density increased. The resistivity is high in Cu thin films deposited without bias voltage. With increasing bias voltage, the resistivity decreased and saturated to nearly bulk value at a bias voltage of -100 V. The resistivity is thought to be influenced by the him density.