This study presents results on the influence of the nature of the filler on the surface properties of polymeric composites produced by co-grinding in a tumbling ball mill. The polymer used in the study was poly(vinyl acetate) which is a model material, while two mineral fillers were tested, i.e., calcium carbonate and silica. The variations of the surface properties of the separately ground and co-ground materials were studied for different grinding times, using the sessile drop method, and the properties were compared to those of matrix-filler blends. The different components of the surface energy were determined by Van Oss decomposition. Grinding generates a large change of the particle surface and especially of the Lewis acid-base energy. These changes depend on the filler nature. In addition, particle agglomeration may be due to an electronic deficit at the particle surface, which is immediately replaced by another particle also possessing an electronic deficit.