A slurry jet erosion apparatus was developed to evaluate the erosion resistance of different materials. The apparatus is based on an air-powered slurry pump; the slurry is accelerated through a nozzle before impingement on the test surface. Contrary to dry erosion conditions, the imposed velocity and impact angle of the particles at the exit of the nozzle are completely modified near the test surface. With the help of streamline analysis, the approximate trajectories of the particles in the fluid were found. The effects on these trajectories of different test parameters such as slurry velocity, particle size, and sand concentration were also studied. It was shown that local impact angle and particle velocity differ at every point of the surface. This investigation on the effect of experimental parameters was applied to the study of the relation between the erosion resistance of metal matrix composites and their microstructures. Particle- and fiber-reinforced composites were tested. Scanning electron microscopy revealed that protection effects from the reinforcement occur in the case of small abrasive particles relative to the area of matrix exposed. For relatively large abrasive, the reinforcement fracture after impact of abrasive particles leads to reduced erosion resistance when compared to erosion conditions resulting in unbroken reinforcement.