Surface finish, surface generation and the influence factors were investigated when high speed milling SiCp/2009Al composites using polycrystalline diamond (PCD) tools. The results showed that the surface roughness Ra0.207-0.542μm and Rz2.02-5.20μm can be attained when tool flank wear VB is less than 0.09mm under the present cutting conditions. With the increasing wear of the cutting tools, the value of the machined surface roughness significantly increased. The machined surfaces included many defects of pits, voids, microcracks, grooves, protuberances, matrix tearing and smearing and so on. The depth of deformation layers were confined to 20-35μm. Among the factors which affected Ra, reinforcement volume fraction was the most significant factor and followed by cutting speed and feed rate. For the side face, the significance order of the factors which affected Rz can be ranged as reinforcement volume fraction, cutting speed, feed rate and radial depth of cut. Material swelling and side flow, tool-workpiece relative vibration, feed rate and tool nose radius, removal mode of SiC particles were the main mechanisms of surface generation.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.