A method of treating a substrate for an electrophotographic photosensitive member by a process comprises the steps of;a) cutting the surface of the substrate to remove the surface in the desired thickness; andb) bringing the cut surface of the substrate into contact with water having a temperature of from 5.degree. C. to 90.degree. C., having a resistivity of not less than 11 M.OMEGA..multidot.cm at 25.degree. C., containing fine particles with a particle diameter of not smaller than 0.2 .mu.m in a quantity of not more than 10,000 particles per milliliter, containing microorganisms in a total viable cell count of not more than 100 per milliliter and containing an organic matter in a quantity of not more than 10 mg per liter, for at least 10 seconds at a pressure of from 1 kg.multidot.f/cm.sup.2 to 300 kg.multidot.f/cm.sup.2.