Diamond-like carbon (DLC) films were deposited on Si substrates by pulsed unbalanced magnetron sputtering with different bias configurations: constant bias and step biasing. The structure, surface morphology, and mechanical properties of the DLC films were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and nanoindentation etc. It has been found that the sp3 content in the DLC films deposited with step biasing is less than that deposited under constant bias. AFM measurements show that the root-mean-square (RMS) surface roughness of the films deposited with step biasing is less than that deposited under constant bias; and the smaller step increase of bias, the lower the RMS roughness. Nanoindentation and residual stress tests indicate that step biasing with 20 min of time intervals and with 20 V of bias reduces the stress of DLC films from 5.8 to 3.5 GPa with little sacrifice of hardness from 13.3 to 12.5 GPa. The results above are useful for the practical application of DLC films.