A simulation model for a tubular solid oxide fuel cell (SOFC) was developed by the object-based approach to calculate the current distribution, gas concentration distribution, and temperature distribution at the steady states and transient operation states. The transient electrical and temperature response to a load change was simulated for the both cells with the diameter of 22mm (standard cell) and the diameter of 2.4mm (micro-tube cell). The time required to reach the new steady state as the operating voltage was changed from 0.7 to 0.5V for the micro-tube cell was found to be 15s, which is much shorter than that of the standard cell.