Poly(4-vinyl pyridine) nano-spheres (P4VP-NS) stabilized poly(vinyl phosphonic acid) (PVPA) membranes were prepared as proton conducting membranes for fuel cells. The acid-base interactions between P4VP-NS and PVPA were utilized to improve the dimensional and thermal stability of PVPA. In this work, the effects of acid-base interactions on proton conductivity and thermal stability were quantitatively determined and discussed based on the results of H-1 magic-angle-spin NMR (H-1 MAS NMR), Fourier transfer infrared spectroscopy (FTIR) and impedance spectroscopy measurements. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.