An object of the present invention is to provide a method for efficiently and highly selectively preparing a composition comprising perfluoropolyether having a hydroxyl group at one terminal at a higher ratio. The present invention provides a method for increasing a ratio of perfluoropolyether having a hydroxyl group at one terminal, relative to a total amount of the perfluoropolyether having a hydroxyl group at one terminal and perfluoropolyether having hydroxyl groups at both terminals in a composition comprising these perfluoropolyethers, wherein the method comprises a step of subjecting the composition to chromatography in which a moving phase is supercritical or subcritical state carbon dioxide of the specific temperature and the specific pressure, and a stationary phase is silica gel to thereby collect a fraction containing the perfluoropolyether having a hydroxyl group at one terminal at a higher ratio. Further, present invention provides for increasing a ratio of perfluoropolyether having a hydroxyl group at one terminal, relative to a total amount of the perfluoropolyether having a hydroxyl group at one terminal, perfluoropolyether having hydroxyl groups at both terminals and perfluoropolyether having no hydroxyl group at any terminal perfluoropolyether, in a composition comprising these perfluoropolyethers, wherein the method comprises a step of subjecting the composition to chromatography in which a moving phase is supercritical or subcritical state carbon dioxide of the specific temperature and the specific pressure, and a stationary phase is silica gel to thereby collect a fraction containing the perfluoropolyether having a hydroxyl group at one terminal at a higher ratio.