In this study, aluminum-based composites reinforced with various amounts of alpha-Si3N4 were produced by powder metallurgy (P/M). The machinability properties of MMCs were determined by means of cutting forces and surface roughness. Machining tests were carried out by using PCD and K10 cutting tools. Increasing of Si3N4 volume fraction in the matrix resulted in a decrease of the surface roughness and turning forces. PCD cutting tools showed better cutting performance than K10 tools. Surface roughness and turning forces were decreased significantly by PCD tool.