This study investigated the effect of a particle diameter and a weight fraction of RB ceramics particles on friction and wear of polyamide 66 composites filled with RB ceramics particles (PA66/RB ceramics composites) sliding against a bearing steel ball under dry condition. RB ceramics particles with a mean diameter of 3, 30, and 150 μm were used as the filler. Weight fractions of RB ceramics particles were 10, 30, and 50 mass% for the mean diameter of the particles of 3 μm, and 30, 50, and 70 mass% for the mean diameters of 30 and 150 μm. The smaller mean diameter and the higher weight fraction of RB ceramics particles provided lower friction coefficients and lower specific wear rates with the PA66/RB ceramics composites. The composite with a mean diameter and a weight fraction of RB ceramics particles of 30 μm and 70 mass% took the lowest friction coefficient of 0.27 among the composites. The composite with a mean diameter and a weight fraction of RB ceramics particles of 3 μm and 50 mass% took the lowest specific wear rate of 1.3 × 10-9mm2/N among the composites, which was equivalent to the specific wear rate of RB ceramics disk.