The cavitation erosion tests of polymeric materials were made by using a magnetostriction vibratory apparatus in pure water. The results were as following : (1)The erosion rate of polymeric materials depends on the test time and increases as the amplitude of the vibration is increased. (2)Alicyclic epoxy resin and orthophthalic unsaturated polyester resin shows brittle fracture caused by the formation and growth of cracks while polypropylene and polyetherether ketone(PEEK) shows ductile fracture caused by plastic deformation and tearing. (3) It is also noted that the erosion resistance of the brittle materials shows a good correlation with fracture toughness, and that of the ductile materials is also correlated well with the degree of crystallinity.