In this study, a new cerium phosphate (CePO4)-doped sulfonated polyether ether ketone (SPEEK) composite membranes were synthesized by using solution casting method with different CePO4 loading. Their performance and durability were investigated for proton exchange membranes fuel cells. Different techniques, namely Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), dynamic mechanical tests (DMA), and electrochemical impedance spectroscopy (EIS) analyses were used to characterize the synthesized membranes. Water uptake (WU) and swelling properties as well as ion exchange capacities (IEC) of synthesized membranes were also determined. Fuel cell performance, durability, and Fenton tests for oxidative stability of the synthesized membranes were also investigated. Experimental results showed that addition of CePO4 up to 10% by weight improved the membrane properties. 10 wt% CePO4-doped membrane possessed a good proton conductivity of 0.242 S/cm at 80 degrees C. Current and power densities of this membrane were obtained as 790 mA/cm(2) and 474 mW/cm(2), respectively, at 0.6 V cell potential and 80 degrees C fuel cell temperature. OCV decrement value of this membrane was 5.93%. When the performance and durability properties of 10% CePO4-doped membrane is compared to commercial Nafion membrane, it could be a good alternative for proton exchange membrane fuel cells.