This work presents investigations of relative cavitation resistance of carbon steel (C45) at the initial stage of erosion, after melting its surface by 6 kW CO2 laser beam. The research work was carried out on the rotating disk facility. Three areas were determined on the surface of investigated sample. Each area was eroded with different intensity. The procedures were elaborated for calculation of resistance of processed surface to plastic deformation under cavitation loading and of relative intensity of cavitation using image analysis of monochromatic picture of eroded surface. The results indicate that increase of cavitation loading intensity results in decrease of relative cavitation resistance.