Despite recent improvement in energy efficiency of diesel engines, more than 50% of the energy input is lost as waste heat in the form of hot exhaust gases, cooling water, and heat lost from hot equipment surfaces. Exhaust pollution from internal combustion engines can potentially result in severe damages on earth atmosphere, including ozone depletion, global warming, and significant health problems. Waste heat recovery based on Rankine cycle has been identified as a potential solution to increase the energy efficiency and consequently to reduce the engine emissions. In this rather low cost technology, waste heat is recovered in a Rankine cycle, aiming to convert mechanical power into electrical power. Output electrical energy is stored in a battery and can be used in electric usages. In this paper, the possibility of using the exhaust heat recovery system without utilizing the heat of other recyclable materials has been investigated, using the organic Rankine cycle (ORC), in order to increase the efficiency of the diesel engine of the bus. Depending on amount of achievable heat of exhaust, in some performance point of diesel engine, the amount of fluid flow rate and output power of Rankine cycle was calculated. Our results exhibit 5.1 KW increase in the diesel engine power resulting in 1.12% increase in energy efficiency in engine part load condition. The output mechanical power from the micro-generator is converted to electrical power and is stored in an energy storage system. The storage energy can be utilized to supply power for electrical equipment such as fans, bulbs, and also phone chargers of passengers.