Si3N4/TiC nanocomposite cutting tool materials were fabricated by adding Si3N4 and Al2O3 nanocomposites with Al2O3 and Y2O3 as additives. The microstructures of materials were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and then wear resistance of Si3N4/TiC nanocomposite cutting tool materials was studied when machining cast iron and quenched steel in continuous dry turning experiments. Micrographs of the worn tools materials were observed with SEM. Results showed that TiC nanoparticles distribute in the matrix grains and lead to the crack deflection as well as crack pinning. Due to TiC nanoparticles and β-Si3N4 quasiwhiskers, the crack trajectories exhibited crack deflection, rod-like grain bridging and pull-out. Wear mode of Si3N4/TiC inserts is mainly abrasive wear with slighter adhesive wear when machining cast iron. The dominant wear patterns during the cutting of quenched steel were adhesion, abrasion, as well as oxidation and diffusion under high temperature.