A method for treating paper which comprises applying to the surface of the paper an aqueous medium containing a sizing composition consisting essentially of 75 to 99.9 wt % polyvinyl alcohol which is at least 95 mole % hydrolyzed and 0.1 to 25 wt % ketene dimer represented by the formula: ##STR1## wherein R and R.sup.1 are the same or different hydrocarbyl groups having 8-30 carbon atoms.