PbS nanofilms with different Cu doping concentrations (0, 1, 2, 3 and 4 at. %) were deposited. The effects of Cu concentration on the structural, morphological, optical and electrical properties of PbS nanofilms were studied. With the increasing dopant content, we find that the crystallite size decreases, the shape of crystal particles changes, the optical band gap increases, the resistivity and carrier concentration change non-monotonously. 2% Cu-doped PbS film has the optimum value of theoretical band gap for absorbing sunlight, and 3% Cu-doped PbS film has the lowest resistivity and the highest carrier concentration.