Poly(amide imide) (PAI) was synthesized using 1,2,4-benzenetricarboxylic anhydride (BTBA) and 4,4'-methylenebis(phenyl isocyanate) (MBPI). SPEEK/PAI blend membranes were prepared and investigated by NMR, GPC, Fr-IR and AFM. The chemical structures of PAI and SPEEK were characterized by using NMR and Fr-IR. The adsorption of the SPEEK/PAI blend membrane of water or methanol solution was also characterized. The significant swelling of the blend membrane in concentrated methanol solution was explained by the solubility parameter. The water diffusion coefficient (D-H2O) was related to the lambda value of the membrane. The SPEEK/PAI blend membrane had a lower proton conductivity and methanol permeability than Nafion. However, the relative selectivity (proton conductivity divided by methanol permeability) of the SPEEK/PAI 70/30 (w/w) blend membrane was 3.46 x 10(4) S s cm(-3), which is closed to that of Nation (3.30 S s cm(-3)). (c) 2006 Elsevier B.V. All rights reserved.