A high temperature polymer electrolyte membrane water electrolyser (PEMWE) was investigated at temperatures between 80 and 130°C and pressures between 0.5 and 4bar. Nanometer size Ru0.7Ir0.3O2 and Pt/C were employed as anode and cathode catalysts respectively. The catalyst coated on membrane (CCM) method was used to fabricate the membrane electrode assemblies. The membrane, oxygen evolution catalysts and MEAs were characterized with SEM, XRD and TEM. The influence of high temperature and pressure was investigated using in situ electrochemical measurements. Increasing temperature and pressure produced higher current densities for oxygen evolution, and smaller terminal voltages. The high temperature PEMWE achieved a voltage of 1.51V at a current density of 1Acm−2, at 130°C and 4bar pressure.