The present paper is concerned with the mechanism of cavitation erosion. A theoretical model for the formation of a single pit produced by a microjet produced by a collapsing cavitation bubble is presented and the model developed to give the average surface slope of the eroded surface as a function of fluid velocity and cavitation number. The model predicts a threshold velocity below which no pitting can occur. A series of erosion experiments were conducted in water tunnel using pure aluminum plates positioned in the sidewall of the tunnel test section subjected to cavitating flow produced by various cavitating sources. The cavitating sources were 25 mm, 20 mm and 10 mm circular cylinder, 10 mm 600 symmetrical wedges, and 20 mm con.-div. wedge. The surface deformation produced on side wall specimens was analyzed by a surface finish measuring device. From the surface profiles, the surface slope and pit radius were computed. The experimental results were compared with the theoretical model and an encouraging agreement was found.