The island uses diesel-power-generation inevitably for its geographical characteristics. It is not economical and more than half of the generated energy is released to the exhaust gas, cooling water and other losses. In order to reduce these losses and improve power generation efficiency, we are studying an organic rankine cycle system using waste heat from a diesel power plant as a heat source. Unlike previous rankine cycle, electric power generation and operation are possible by using the low heat source and capacity. Cycle design and demonstration-operation logic are required to proper the range of waste heat temperature and capacity. Also, depending on the efficiency of each component, the overall efficiency may change greatly, so it requires to optimize of operating conditions of various BOP. It is necessary to establish optimization and operating conditions of the system for each element with modeling and numerical study of the whole system. In this research, heat source analysis and BOP design were carried out in order to apply the 20 kw / 30 kw ORC system to Heuksan island 1MW-diesel power plant. We have developed a heat-connecting technique that thermally connects the heat exhaust piping at the final end and the evaporator of the ORC system. The demonstration experiment is conducted sharing the waste heat source with 20 kW and 30 kW ORC system. In this paper, we presented the waste heat analysis and the demonstration operation result of Heuksan island power plant.