A thermoeconomic analysis of an ocean thermal energy conversion (OTEC) system was performed using the modified productive structure analysis (MOPSA) method. In this analysis, the unit cost of electricity from the 20-kW OTEC pilot plant built and operated at the Korea Research Institute of Ships and Ocean Engineering was estimated. The unit cost of electricity from the OTEC plant with thermal efficiency of 0.66% is approximately $0.363/kWh. The unit cost of electricity of the OTEC plant increases linearly with the unit cost of supplied heat to the evaporator and increases inversely to the exergy efficiency of the system independently. The OTEC system was found to be economically viable renewable energy source in the regions where the temperature of warm sea water remains to be 25 °C and the condenser effluent from a power plant is available.