In a cavitation tunnel, it is difficult to produce so intense cavitation that may cause erosion on the back of a propeller blade or a hydrofoil. To make cavitation erosion experiment possible, some special experimental techniques should be derived such as aluminium erosion test, paint test etc. Authors have studied the effect of cavitation number, fluid velocity, size and material of hydrofoil on the cavitation erosion by aluminium erosion test and paint test. This paper reports the result of those tests for three types of two-dimensional hydrofoils (NACA-0015, NACA-16015, and NACA-4415). The erosion intensity is more influenced by the unsteadiness of cavity than the difference of hydrofoils. When the fluctuation of cavity is little, a peak of erosion is clearly observed at a little downstream position of the cavity end. On the contrary, when the fluctuation is large, the erosion peak becomes lower, but the range and intensity of erosion becomes wider and more intense. This paper also treats the calculation of erosion pit formation by the axisymmetric elastic-plastic analysis using the finite element method. The rim of a pit, which is sometimes observed at an actual case, can be successfully reproduced by the calculation of the simple compressive load on the solid surface. Based on those analysis, a new estimating method is proposed to scale the erosion amount for various materials. Finally the influence of mechanical properties of material on the erosion is discussed.