A series of novel poly (2,5-benzimidazole)-grafted montmorillonite (ABPBI-MMT) and sulfonated poly vinyl alcohol (SPVA) composite membranes have been prepared via solution casting method which were further doped with phosphoric acid. The structure of composite membranes has been studied using FTIR, XRD and SEM. The effect of ABPBI-MMT on the water uptake (WU), proton conductivity, mechanical and chemical stability of the resultant membranes has been examined before and after phosphoric acid (PA) doping. This study flaunted that the introduction of ABPBI-MMT into SPVA decreased the WU of pristine polymer matrix as a result of acid-base interaction between the sulfonic acid and benzimidazole groups. However, after PA doping, the WU of the membranes has tremendously boosted. Initially, the influence of ABPBI grafted clay on proton conductivities of SPVA membranes has been studied along with the analysis of PA doping effect on membrane conductivity with fuel cell performance. Furthermore, the proton conductivities of PA doped, and un-doped composite membranes have been studied at high temperatures ranging from 100 to 140 degrees C under 0% RH. The PA-doped composite membranes show enhanced conductivity values (0.0075 Scm(-1)) at 140 degrees C even with 0% RH. The maximum proton conductivity of 0.157 Scm(-1) and peak power density of 1100 mWcm(2) have been obtained at 140 degrees C under 100% RH with 15PBMPP composite membranes. These results indicate that the newly prepared PA-doped PEMs are an excellent candidates for high-temperature PEM fuel cell application. (c) 2020 Elsevier Ltd. All rights reserved.