The growing demand of power has made the power plants of scientific interest, but most of the power plants are designed by the energetic performance criteria based on first law of thermodynamics only. The real useful energy loss cannot be justified by the first law of thermodynamics, because it does not differentiate between the quality and quantity of energy. The objective of this paper is to perform the energy, exergy analysis for the Besat steam power plant located in Tehran.The results show that energy losses have mainly occurred in the condenser where around 77% of the total power plant energy losses are lost to the environment. Nevertheless, the exergy destruction rate of the boiler is higher than the exergy destruction rates of the other components. It is due to the fact that the combustion reaction and its high temperature are the most significant sources of exergy destruction in the boiler system. The second large exergy destruction occurs in the turbine system. So significant improvements potential exist in the boiler and turbine unit.