Method for fabricating a substrate comprising a nanostructured surface for an organic light emitting diode OLED, in which a layer of an organic resin or of a mineral material having a first nanostructuration is prepared by nano-imprint; the organic resin or mineral material is heated to a temperature equal to or higher than its glass transition temperature Tg or its melting point, and the organic resin or the mineral material is maintained at this temperature for a time tR called annealing time, whereby the organic resin or the mineral material flows and the first nanostructuration of the layer of organic resin or of mineral material is modified to produce a second nanostructuration; the organic resin or the mineral material is cooled.