Abstract X.p.s. was used to study the surface composition of dealuminated zeolites including the parent zeolite NaY and ammonium exchanged samples. The dealumination was performed by thermochemical treatment of the ammonium exchanged samples and by extraction with EDTA. For NaY and the ammonium exchanged samples no difference in the Al Si and Na Si ratios between bulk and surface is observed. The Al Si ratios of the external layers show for the thermochemically dealuminated zeolites a strong dependence on the temperature of treatment and can become, at high temperatures, up to three times higher than that of the bulk. The enrichment of aluminium in the surface is interpreted as accumulation of non-framework aluminium species which migrate out of the micropore system towards the zeolite surface. The aluminium extraction with EDTA favours the external layers of the crystals.