The anode-operating parameters are significantly important to enhance the performance of an air-cooled proton exchange membrane fuel cell (AO-PEMFC) under natural conditions. To determine desirable anode-operating parameters with optimum cell performance, the effects of hydrogen pressure: 10-90 kPa, temperature: 30-70 degrees C, humidity: 0 and 100%, and stoichiometry ratio: 1.4-2.0 were systematically investigated. Besides, the single-cell and 3-cell stack of AO-PEMFC was built to verify the difference. The polarization curve, electrochemical impedance spectra, and the cathode outlet surface temperature distribution were obtained to ascertain the performance and main loss source of AO-PEMFCs. The test results show that the anodeoperating parameters mainly affect the membrane resistance and water flooding. Through the comparison of various parameters, the appropriate operating parameters such as H-2 pressure, temperature, humidity, and the stoichiometry ratio were identified to be 5070 kPa, 30-50 degrees C, low humidity, and 1.8, respectively. It is shown that the AO-PEMFCs operating with appropriate anode-operating parameters can provide higher power density for portable applications.