A novel method for evaluation of ion-selective electrode membranes was reported with the proton spin-spin relaxation time T(2) by pulsed NMR. The proton spin-spin relaxation time T(2) measurements provided valuable information about properties of the whole membrane matrix. The softer potentiometric liquid membrane possessed a large fraction F(L) providing relatively longer T(2) value. Pulsed NMR method can quantify the degree of the plasticization of ion-selective electrode membranes.