Sulfonated polyimide (SPI) based membranes for proton exchange membrane fuel cells (PEMFC) have been synthesized by using a one-step high temperature polymerization method. The membranes were characterized with Fourier transform infrared spectra (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC); water uptake, ion-exchange capacity, proton conductivity and mechanical stability were tested. The results showed that the membranes had good thermal and mechanical stability and exhibited good performance when they were assembled into membrane electrode assemblies (MEAs). Fuel cell testing was performed. The SPI copolymer based MEA was tested under different hydrogen flow rates to compare with the commercially available Nafion® based MEA.