For Co films on Pd(1 1 0) covered with Au, the polar hystersis loops measured at 120 K are reversed below 2.7 ML with respect to those of thicker Co films, which is due to the negative contribution to polar Kerr rotation from the Co/Pd interface dominating in this thickness range over the positive polar Kerr rotation from the non-interface part of the Co film. Near the film thickness where the Kerr rotation changes sign a remarkable combination of two loops (normal and reversed) of two slightly different coercivities is observed regarded as a superposition of two different magneto-optical contributions corresponding to thinner and thicker parts of the Co film. The thin and thick film areas could have different temperature dependence of magnetization (the negative contribution could depend stronger on temperature since it is related to the thinner part of the film), leading to the increasing total polar Kerr rotation with increasing temperature.