In this paper, the authers describe an experimental investigation of the cavitation damage on a two-dimensional hydrofoil -NACA 16-021 section made of pure aluminum-tested in a venturi type cavitation tunnel. Linearized theory of cavity flow was used along with the equation of bubble radius to predict the cavitation erosion intensity. The following conclusions are obtained : 1) Weight losses caused by cavitation erosion could be devided into 3 zones : Incubation, Accumulation and Attenuation zone, respectively. On the other hand, surface roughness increased linearly with the exposure time to cavitation even in the incubation period. 2) Measurement of the surface roughness is an useful method to evaluate cavitation damage. 3) The maximum erosion rate appears at a certain cavitation number. The same tendency can be obtained by the above mentioned theoretical analysis. 4) The paint test results agree with that of the measurement of surface roughness increase. 5) The plastic deformation caused by cavity collapses was simulated using the two-dimensional elastic-plastic analysis by FEM. The calculated result shows a qualitative agreement with the exprimental results. But the raised rim around a pit which is observed on the eroded surface, is not obtained by the FEM calculation.