A poly(R 1 R 2 R 3 )–N + /H 3 PO 4 composite membrane has been developed for use in a polymer electrolyte fuel cell (PEMFC). The quaternized polysulfone (QNPSU) membrane doped with H 3 PO 4 showed high proton conductivity (0.12Scm −1 ) at 160°C and gave good performance in a single fuel cell tests. The peak power density with the QNPSU/H 3 PO 4 composite membrane (at 150°C, with dry H 2 /O 2 ) was greater than 0.7Wcm −2 . The effect of the phosphoric acid doping level on fuel cell performances with the QNPSU membrane was investigated. The data show that the QNPSU/H 3 PO 4 composite membrane is promising for higher temperature PEMFC applications. The study demonstrated that the poly(R 1 R 2 R 3 )–N + /H 3 PO 4 composite system produced an effective method to connect phosphoric acid to a non-conducting polymer structure, to produce a promising membrane for phosphoric acid polymer electrolyte membrane fuel cells.