Ultra-precision turning tests on SiCp/2024Al and SiCp/ZL101A composites were carried out to investigate the surface quality using single point diamond tools (SPDT) and polycrystalline diamond (PCD) cutters. Examined by SEM, the machined surfaces took on many defects such as pits, voids, microcracks, grooves, protuberances, matrix tearing and so on. The results showed that surface quality debased with increasing feed rate or using of high volume fraction materials. Dry cutting would deteriorate the surface finish. It was also pointed out that SPDT outperformed PCD tools although they produced the same surface roughness Ra. Microhardness measuring showed that the deformation layer was extended to 8–16μm below the machined surface.