Experimental purpose is to test gravity influence on water discharged in PEM fuel cell cathode. Through changing the way of placement of the cathode and anode, it takes adjusting the electronic load to test the output of voltage and current. Corresponding to the position of the cathode-upward and the anode-upward, different humidification condition, draws the polarization curve using the voltage and current density. According to the placing position of the cathode and anode, cell temperature, humidification temperature of the cathode and anode gas, 4 groups of experimental results are obtained. The experimental conclusion is: when a PEM fuel cell is placed anode-upward, gravity is advantageous to discharge the liquid water in PEM fuel cell cathode. On the contrary, gravity is disadvantageous to discharge the liquid water. (C) 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu.