A numerical analysis was performed to study PEMFC characteristics depending on GDL porosity and the inlet direction in cathode gas channel using the FLUENT. As GDL porosity increases, temperature increases. For the both of co-flow and counter-flow cases, temperature is higher near the hydrogen inlet region where the chemical reaction rate is high. As GDL porosity increases, current density increases. In overall, counter-flow case gives higher current density compared to co-flow case for the same operating conditions. However, the difference in the current density is not high. The water mass fraction is also higher near the hydrogen inlet region due to the chemical reaction rate for the both of co-flow and counter-flow cases.