The aim of this feasibility study is the practical implementation of a small output Organic Rankine Cycle (ORC) less than 20kW. In this study, the evaluation method of a turbine efficiency which is the major component of the ORC was examined, moreover, the performance of the ORC was evaluated based on the turbine efficiency using the heat source of Obama hot spring in Unzen-City. The outlet temperature of the turbine applied the insulation treatment was almost same the temperature without the treatment. This result indicated the influence of the heat absorption on the turbine of the ambient temperature for the working fluid was small. The adiabatic efficiency in the turbine test itself was about 7.9%. It indicated the working fluid absorbed the mechanical frictional heat generated inside the turbine. In the verification test of Obama hot spring, the thermal efficiency of the prototype ORC was 2.4%. The turbine efficiency at the operating point in the urbine test was 21.2%, whereas the turbine efficiency in the ORC verification test was 19.2%.