The Kansai Electric Power Company, Inc. and Mitsubishi Materials Corporation started a joint research project for developing intermediate temperature (600°C to 800°C) solid oxide fuel cells (IT-SOFC) in 2001. High performance disk-type cells with lanthanum gallate-based electrolyte and a seal-less cell-stack design enable high efficiency operation at temperatures below 800°C. The development of 10 kW-class CHP system under a project supported by NEDO (New Energy and Industrial Technology Development Organization) was started in FY2004. In 2007, the performance test of the 10 kW-class system using town gas as fuel was undertaken. In this test, the electrical efficiency of 41 %HHV on AC power output of 10 kW and the overall efficiency of 82%HHV by recovering 60°C hot water were achieved. And the voltage degradation rate per 1, 000 hours was 1.08% after 3, 000 hours operation during the field test of the 10 kW-class system. Furthermore, after making some refinements to enhance the performance of 10 kW-class module, the second long-term stability test for 3, 000 hours was carried out in 2008. Efforts to enhance cell and module durability were made with 1 kW-class modules operated for 5, 000 hours, and with the cell-stack units operated for 15, 000 hours. The voltage degradation rates per 1, 000 hours were 0.51 % for the 1 kW-class modules, and 0.23-0.48% for the cell-stack units.