Abstract: The invention concerns a method and an installation for purifying impure helium. Said method consists in subjecting the helium to at least two successive steps: (a) cryogenic refrigeration of impure helium so as to eliminate by condensation at least part of the main impurities it contains and recuperating helium with intermediate purity containing residual impurities; and (b) permeation of at least part of the helium with intermediate purity derived form step (a) so as to eliminate at least part of said residual impurities and recuperating helium with final purity higher than said intermediate purity. Said method and said installation are useful for purifying impure helium recuperated at the output of an optical fibre cooling chamber, prior to the reintroduction of the resulting purified helium into said chamber so as to recycle the helium.