An experimental study of frictional wear of rock, conducted with a rotary apparatus, shows that wear loss, the loss of material from the interface of two bodies during frictional sliding, is a function of normal stress and the initial roughness of the sliding surface. Under a given normal stress and initial roughness, the wear loss-sliding displacement relationship indicates that wear rate is initially high and then gradually decreases to a constant value. The wear process results in an evolution of the surface topography as shown from profilometer measurements of the surface at different stages of wear. The distribution of asperity heights shows that the top of the sliding surface is progressively truncated with accumulated slip. Based on a model of two rough surfaces in elastic contact, a numerical model for wear can describe wear in two different stages: a transient stage and a steady state stage. In the transient stage, the wear mechanism is interpreted as shearing off of interlocking asperities. The total contribution by this mechanism is proportional to the overlapping volume of the asperities, V*, which is related to the initial roughness as well as the normal stress. In the steady state stage, wear is almost linear with displacement and the wear rate is proportional to the real area of contact between the two rough surfaces. Introducing a parameter h, the interlocking distance between two contacting asperities, provides a better understanding of the wear process with different surface roughnesses. Below a critical value of interlocking distance hc, the contacting asperities deform elastically and slide over each other. When h>hc, they tend to shear off. The model predicts the effects of normal stress and initial roughness, and its predictions are in good agreement with the experimental results.