Anode supported micro tubular SOFC has been studied because it has high energy density and thermal shock resistance. Relationship between the performance of micro tubular cells and thickness of the GDC electrolyte was examined at temperatures between 500 degrees C and 650 degrees C. Performance of the cell with 15.5 mu m thick electrolyte was higher than the cell with 40 mu m thick at lower temperatures, but lower at higher temperatures. At lower temperatures, ohmic loss is dominant in the voltage drop, but at higher temperatures, leakage of electron through the GDC electrolyte is main reason for the voltage drop.