The influence of the particle size of fillers on the frictional wear properties of dental composite resins has been investigated. Five kinds of silica fillers with mean particle sizes of 0.5, 3.3, 4.3, 7.9, and 15.5 mum are used in this study. The filler volume is kept constant at 70 wt%. The coefficient of friction between the abrasive and the specimen was determined by a frictional wear device employing a rotating wheel. After the test, the wear depth was measured by a surface profilometer and the wear surface was observed by FE-SEM. The results demonstrate that the coefficient of friction and the wear depth increase with an increase in the particle size of the filler of composite resins. In addition, a linear correlation between the coefficient of friction and wear depth was found.