Steam electrolysis was carried out using a micro tubular ceramic reactor which has the cell configurations as follows; La 0.6Sr 0.4Co 0.2Fe 0.8O 3-d (LSCF) - Ce 0.8Gd 0.2O 1.9 (CGO) electrode / CGO buffer layer / (ZrO 2) 0.89(Sc 2O 3) 0.1 (CeO 2) 0.01 (ScSZ) electrolyte / Ni-ScSZ electrode supporting tube. 10%H 2-Ar mixture gas was used as steam carrier gas, and 18% steam was supplied to inside of the ceramic reactors. The cell voltage 1.43V at 0.1Acm -2 was observed at 650 °C. During the steam electrolysis, hydrogen production has proportionally increased with current density increasing, and heat generation from low current density was observed by electro-chemical technique. Voids and incursion of Zr were confirmed in CGO buffer layer. Such factors nearby surface probably caused increase in the ohmic resistance and electrode over potential.