Cross-linked sulfonated poly (ether ether ketone) (SPEEK)/reactive organoclay (Cloisite-30B) nanocomposite membranes were fabricated using 1,4-bis (hydroxymethyl) benzene (BHMB) as cross-linker and Cloisite-30B organoclay as the pseudo cross-linker. The cross-linked SPEEK/clay nanocomposite membranes were prepared via solution intercalation method. Participation of reactive organoclay in the cross-linking process was established from ion exchange capacity (IEC) measurements and FTIR studies. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) confirmed mixed clay dispersion morphology of intercalation and partial exfoliation of the clay platelets in the cross-linked SPEEK/clay nanocomposite membrane. The cross-linked SPEEK/clay nanocomposite membranes were characterized for their thermal and physical properties as a function of clay loading. The characteristics of the cross-linked nanocomposite membranes were then compared with pristine SPEEK membrane. The membrane stability, i.e. liquid uptake in water and in aqueous methanol solution, oxidative stability as well as mechanical and thermal stability were found to significantly improve with incorporation of reactive organoclay into the cross-linked SPEEK polymer matrix, without affecting the protonic conductivity appreciably. (C) 2011 Published by Elsevier B.V.