PROBLEM TO BE SOLVED: To obtain plastic molded articles having high transparency and high oxygen permeability, and good wettability by water and, simultaneously, excellent mechanical properties as well. SOLUTION: The surface treatment of a plastic molded article can be conducted by dipping the plastic molded article in a solution or a suspension of a polymer having at least one kind of a 'convertible group', and then converting the substituent ('convertible group') which the polymer has into at least one functional group selected from an acidic functional group, a basic functional group, and a hydroxy group.
