In some types of diesel engines, pitting damage troubles have been sometimes experienced, which seems to be related with Cavitation due to vibration of cylinder liners being excited by the impactive force from piston motion. In this study, the dynamical behaviors of cylinder liner of the marine use trunk type and two-stroke diesel engine whose bore is 350φ have been measured and discussed from the viewpoint of cavitation erosion. In our experiments, the cylinder liner deflection caused by impactive force from piston showed the value more than 0.1 mm at each cycle, and this deflection was followed by excited vibration of cylinder which caused the pressure fluctuation of cooling water in jacket enough to initiate cavitation. Cavity motion was observed directly at the same time to make our estimation more sure. On the other hand, the studies on each factor considered to have dominant influence on cavitation erosion have been carried out in simple model scale but in detail. Magnetstrictive vibratory test showed us that if the vibration amplitude is kept within 0.04 mm, cylinder liners will be successfully prevented from cavitation erosion. Addition of soluble oil to cooling water was found to have remarkable effect on the reduction of caviration erosion, the reason of which was in the variation of surface tension of water by the addition of soluble oil.