A Proton Exchange Membrane (PEM) fuel cell has been undergoing development in Thailand for five years. A fuel cell testing station has been set up to measure and control the mass flow rate of hydrogen (H2) and oxygen (O2), cell temperature, backing pressure and gas humidity. An interfacial unit and software have also been developed to provide significant data instantly. Membrane Electrode Assembly (MEA) was fabricated using solid electrolyte membrane, Nafion® 115, and platinum catalyst 20 wt% on carbon particle. The study is devoted to test PEM fuel cell performance, by analyzing the current density and voltage characteristics (I-V curve) and the current density and power density (I-P) curve, at various soaking conditions. It is found that the operating conditions which yield the best cell performance are the following: relative humidity of hydrogen at 80% to 90%, and relative humidity of oxygen at 50% to 60%; mass flow rate of hydrogen at 100 standard cubic centimeters per minute (sccm/min) and mass flow rate of oxygen at 140 sccm/min. These operating conditions yielded the maximum power density at about 150 milliwatts per square centimeters (mW/cm2) in reaction area of 25 cm3. The performance of aluminum alloy (94% Al and 6% Si) as the gas flow field in place of graphite was also investigated. It is found that the gas flow field made of aluminum alloy yielded lower performance than that of graphite because of the oxide film at the surface of the aluminum alloy.