Hydrogen production by the sulfur-iodine (SI) process, with an electrodialysis (ED) stack embedded in the HI decomposition section (SEC3) to concentrate HI in the HIx solution and overcome the pseudo-azeotrope, was conducted under pressurized conditions. The HIx solution of H2O/HI = 5.63-6.13 and I-2/HI = 0.57-1.97 was supplied to the SEC3. HI gas was concentrated in a packed distillation column and decomposed over Pt/Al2O3. The experimental results of distillation column operation under different feed rates and HIx compositions are reported. The raffinate from the column showed a pseudo-azeotropic Hlx mixture, as predicted in previous research. The dynamic responses of the ED stack were examined during the start-up period according to the HIx feed composition at the anode inlet. The ED voltage changed with the I-2 concentration in the inlet flow. The proton transport number (t(+)) and electro-osmosis coefficient (beta) were estimated for the ED stack during the operations. Hydrogen production ranged from 18.3 to 50 L/h, depending on the operating conditions and HIx feed composition. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.