A full three-dimensional, single phase computational fluid dynamics model of a proton exchange membrane fuel cell (PEMFC) with both the gas distribution flow channels and the Membrane Electrode Assembly (MEA) has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region are developed and numerically solved using a finite volume based computational fluid dynamics technique. In this research, some important parameters such as variation of oxygen and water mass fraction, liquid water activity and the membrane protonic conductivity have been presented at the entry and exit regions of the cell. The numerical results indicated that, at lower cell voltage (0.6v) which corresponds to higher current density, the hydrogen and oxygen consumption and, accordingly water production is high. Finally the numerical results of the proposed CFD model are compared with the available experimental data that represent good agreement.