Cu thin films were deposited on Si(100) substrates using direct current (DC) magnetron sputtering. We focused on the effect of sputtering DC power on the electrical, structural properties, and the nucleation and growth of Cu films during the initial stage of sputtering. The Cu films deposited at higher sputtering power showed strong crystallinity, low electrical resistivity in comparison with the Cu films deposited at lower sputtering power. Concerning the nucleation and growth of Cu films during initial stage of magnetron sputtering, it was found that the progress of the nucleation and growth of the Cu films at higher sputtering is much faster than those of the Cu films at lower sputtering power even though they have a similar nucleation and growth mechanism, and their relation to resultant microstructure was confirmed by atomic force microscopy.