Using a scanning electron microscope (SEM) and an electron probe surface roughness analyzer (ERA), we conducted the in vivo study of the effect of various filler components on the wear of composite resins. Experimental light-cured composite resins were prepared employing three different filler components; -(1) Silica type, (2) Strontium type, and (3) Barium type. The filler content for all three types was 80 wt%, with the mean particlesize being 2.6 microns in diameter. The resin monomers consisted of 40 wt% Bis-GMA, 40 wt% TEGDMA and 20 wt% UTMA. These materials were placed in 2 mm diameter cylindrical cavities located in the OCA (occlusal contact area) or the CFA (contact free area) of cast crowns temporarily set in a volunteer patient's mouth. The crowns were removed at monthly intervals for longitudinal SEM observation. After two months, worn surfaces were also analyzed by ERA. The result showed that the wear patterns of the composites were characterized by the filler components, especially in the OCA.