Abstract: In order to make hard and soft contact lenses having a pore diameter and a pore density optimum for use as oxygen permeable contact lenses, the contact lens after molding is subjected to irradiation of a polyvalent heavy ion beam having a mass number of 2 to 100 (preferably 10 to 80) and an ion energy of 10M eV (preferably 50M eV) or higher, at an ion radiation density of 10 to 10.sup.9 ions/cm.sup.2 (preferably 10.sub.2 to 10.sub.5 ions/cm.sup.2) and thereafter ultrasonically etched (preferably at 10 to 50 MHz) at a temperature of 4 to 50.degree. C. (preferably 10.degree. to 30.degree. C.) in the presence of chloroacetic acid (preferably tricholoracetic acid).