In this study, the performance of a PEM fuel cell is investigated experimentally. Some parameters such as input oxygen temperature, input hydrogen temperature, cell temperature, input pressure, oxygen flow rate and hydrogen flow rate affect the performance of the cell. A series of experiments are carried out to investigate the influence of the above parameters on the polarization curve under the normal conditions. A PEM fuel cell with 25 cm2 active area and Nafion 117 membrane for the anode and cathode is employed as a membrane electrode assembly. The results show that increase in the operating temperature of the cell and inlet gases and pressure can enhance the cell performance. Also the results show that when the oxygen flow rate is at 0.9 L/min and the hydrogen flow rate is at 0.5 L/min the performance of the cell increases.