Flat-tubular solid oxide electrolysis cells have been manufactured with a ceramic interconnector in a body to minimize the stack volume and eliminate metallic components. The NiO-YSZ supports are prepared by the extrusion method, and the other cell components, which included the electrolyte, air electrode, and ceramic interconnector, are fabricated by slurry coating methods. The active area of a single cell is 30 cm(2), and the gas tightness of the stack is checked in the range below 2 bars. The effects of the operating conditions on the performance of a solid oxide electrolysis stack are investigated using electrochemical impedance spectroscopy and the I-V test. Consequently, it is confirmed that sufficient steam content stimulates the electrochemical splitting of water and decreases the activation energy for water electrolysis at a high temperature. In our 3-cell stack test, the hydrogen production rate is 4.1 lh(-1), and the total hydrogen production was 144.321 during 37.1 h of operation. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.