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In this study, the relative humidity of the gases in the PEM fuel cell was changed and its effect on electro-osmotic flow was investigated. ‎By changing the humidity on both sides of the fuel cell and using the water balance equations, the values of the electro-osmotic flow, ‎electro-osmotic coefficient and net drag in different humidity levels were found. Results showed that variations of the electro-osmotic ‎flow changed linearly by anode and cathode humidity to the special humidity and after that not much variation was seen. In addition, the ‎results revealed that humidity change at anode had more desirable effect than the cathode. For example, at 70% anode humidity and 35% ‎cathode humidity with the current of 5A, the value of electro-osmotic flow was obtained as 2.66639E-06 mol/cm2.s, while in the former ‎‎35% and the latter 70% with the same current, this value was recorded as 2.56418E-06 mol/cm2.s. In addition, results showed that the‎‏ ‏variations of the electro-osmotic coefficient changed linearly by humidity. It was determined the current change of fuel cell has not so ‎effect on the curves of electro-osmotic coefficient. The electro-osmotic coefficients varied between 0.636001 and 1.632476, which were ‎in a good agreement with the values obtained in other related papers. In addition, the variations of the net drag in respect of humidity were ‎investigated, too. It was determined that the net drag changed linearly by the cathode humidity with positive slope, but its variations by ‎the anode humidity were linearly with negative slope.‎