An intermediate temperature solid oxide fuel cell (SOFC) is developed and its performance is investigated experimentally and theoretically. In the experimental program, a gadolinium doped ceria based membrane electrode group is developed with the tape casting and screen printing methodology and characterized. An experimental setup is devised for the performance measurement of SOFCs and the performance of produced cells is investigated over a range of parameters including the electrolyte thickness, the sintering temperature, the operation temperature etc. The experimental setup is then further modified to measure the temperature distribution in the large SOFC single cells. The effects of operating parameters on the temperature distribution are investigated and the parameter spaces leading high efficiency without cracking the ceramic membrane are identified. In theoretical study a mathematical model is developed to represent the fluid flow, the heat transfer, the species transport and the electrochemical reaction in intermediate temperature of solid oxide fuel cells.The differential equations are solved numerically with a commercial CFD code which employs a control volume based approach. The temperature distribution and species distribution during theSOFC operation is analyzed. The effects of operation parameters on critical SOFC characteristics and the performance are numerically investigated over a range of parameter space. The experimental and numerical results are compared to validate the mathematical model. The mathematical model is found to agree reasonable with experimental data.