In this research, the operating parameters of proton exchange membrane (PEM) electrolyzer are optimized in order to decrease the required input voltage using Taguchi method. The considered parameters include the operating temperature, the pressure of cathode and anode, membrane water content, membrane thickness, and cathode and anode exchange current density. First, a thermodynamic model is developed for the PEM electrolyzer, and then the Taguchi method is applied for optimization of the electrolyzer performance. The signal to noise ratio (SNR) and the analysis of variance (ANOVA) method are also performed to determine the contribution ratio of effective parameters. The results reveal that the optimal condition is achieved at maximum working temperature, membrane water content, and cathode and anode exchange current density and at minimum membrane thickness, cathode pressure, and anode pressure. The anode exchange current density has considerable effect on the electrolyzer voltage with contribution of 67.15% while the membrane water content and the anode pressure have a minor influence with contribution of 1.1% and 0.42%, respectively. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.