An inorganic-organic composite membrane composed of Fe0.4Ta0.5P2O7 (FTPO) and sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) is prepared and characterized. To gain satisfaction of both the proton conductivity and mechanical strength in composite membranes, the optimal content of sSEBS was determined to be 30 wt%, which resulted in high proton conductivities of approximately 0.01 S cm(-1) between 50 and 150 degrees C even under an unhumidified condition, a tensile strength of 4.1 MPa, and an elongation at break of 613%. A homogeneous distribution of the FTPO particles in the matrix was achieved at the composite membrane thickness greater than 50 mu M, providing gas-impermeability and low area-specific resistance (ASR) of the membrane (0.17 Omega cm(2) at 150 degrees C and H2O vapor concentration of 30.8 vol%). Fuel cell tests using the composite membrane provided peak power densities of 265 and 303 mW cm(-2) at 150 degrees C under an unhumidified condition and at a H2O vapor concentration of 30.8 vol%, respectively. (C) 2013 Elsevier Ltd. All rights reserved.