For the purpose of developing high performance tribomaterials for mechanical sliding parts such as gears, bearings and so on, nanosized calcium carbonate (nano-CaCO3) filled polyamide 66 (PA66) nanocomposites were investigated. The nano-CaCO3 was a kind of precipitated (colloid typed) CaCO3, and its average particle size was 0.08 and 0.04 m. Surface treatment was performed by fatty acid on nano-CaCO3 and its volume fraction was varied from 1 to 20 vol.%. These nanocomposites were melt-mixed by a twin screw extruder and injection-molded. Tribological properties were measured by two types of sliding wear testers such as ring-on-plate type and ball-on-plate type under dry condition. The counterface, worn surface and wear debris were observed by digital microscope and scanning electron microscope. It was found that nano-CaCO3 has a good effect on the tribological properties, although the frictional coefficient and specific wear rate was differed for the volume fraction and the type of sliding wear modes. This is attributed to the change of wear mechanisms, which is the change of form of the transfer films on the counterface and the size of wear debris. It follows from these results that PA66/nano-CaCO3 nanocomposites may be possible to be the high performance tribomaterials.