In the present study, new nanocomposite membranes based on sulfonated poly (1,4-phenylene ether-ether sulfone), BaZr0.9Y0.1O3-delta and SrCe0.9Yb0.1O3-delta doped-perovskite nanoparticles have been prepared. The BaZr0.9Y0.1O3-delta and SrCe0.9Yb0.1O3-delta doped-perovskite nanoparticles enhance the thermal and mechanical stability of the nanocomposite membranes. Besides, the water uptake of the nanocomposite membranes increases and so, the proton conductivity increase. Substitution of Ce4+ by Yb3+ in the SrCe0.9Yb0.1O3-delta doped-perovskite nanoparticles and the substitution of Zr4+ by Y3+ in the BaZr0.9Y0.1O3-delta doped-perovskite nanoparticles produce oxygen vacancies and decrease the coulombic repulsion between protons and positive ions. The oxygen vacancies in BaZr0.9Y0.1O3-delta and SrCe0.9Yb0.1O3-delta doped-perovskite nanoparticles act as water and protons trap, and so increase the rotational motion of the proton and the proton conductivity in the nanocomposite membranes. The highest proton conductivity for the nanocomposite membranes containing the BaZr0.9Y0.1O3-delta and SrCe0.9Yb0.1O3-delta doped-perovskite nanoparticles are 126 mS cm(-1) and 117 mS cm(-1), respectively, at 80 degrees C and 95% RH. The long lifetime of the proton conductivity and considerable fuel cell performance, 0.61 W cm(-2) power density at 0.5 V, of the nanocomposite membranes confirm their high potential for application in the PEM fuel cells. (C) 2019 The Electrochemical Society.