AbstractProton‐conducting membranes based on sulphonated poly (ether ether ketone) (SPEEK) polymer matrix and tin dioxide have been synthesized. Their local structure has been studied by FTIR and XRD whereas their structural features at nanometer scale has been investigated by Small‐Angle X‐ray Scattering (SAXS) and transmission electron microscopy (TEM). SAXS and TEM results show that incorporation of the inorganic particles in SPEEK promotes dispersion of the hydrophilic sulfonic groups in the polymer matrix, inhibiting the formation of the water‐filled ionic clusters usually observed in hydrated SPEEK membranes. The changes in SPEEK nanostructure are induced by incorporation of particles modified by Tiron that promotes the connectivity between hydrated channels and reduces diffusion of alcohol, as evidenced by permeability measurements. The resulting increase of proton conductivity compared to pristine SPEEK, particularly at medium temperature (80°C), combined to an improved dimensional stability, make this family of membranes very promising for future applications in fuel cell.