In Kitakyushu Science and Research Park, a new district energy system has been introduced. In this study, we chose this systemas a case study and have carried out an analysis on the efficiency of the power generation and heat release utilization of the fuel cell and gas engine in summer by using the recorded data. The results can be summarized as follows; 1) Although the power generation efficiencies of the gas engine and fuel cell are a little bit lower than the standard designated value, they are almost running at stable condition. 2) The collected heat energy is lower than the designated value. The heat release utilization, which is used for cooling and hot water, is fairly low. Considering the efficient use of energy, it is a key to have a good use of heat release when we introduce a district energy system. 3) The discarded heat energy of the system is very big in this investigation when evaluating the system as a whole. It is fundamental to the future of energy conservation to use primary energy more efficiently.