An Organic Rankine Cycle (ORC) system used in the Internal Combustion Engine (ICE) exhaust heat recovery was proposed and techno-economically analyzed based on various working fluids. It is significant to recover ICE exhaust heat (about one third of energy generated from the fuel) by ORC system. In this paper, the suitable working fluids have been screened and recommended for the ORC system, among 20 fluids (boiling point temperature range from -51.60 to 32.05 degrees C) analyzed on the rated condition of one popular commercial diesel generator set. The cycle parameters, including the thermal efficiency (eta(th)), the expansion ratio (v(2)/v(1)), the net power output per unit mass flow rate of hot exhaust (P-net), the ratio of total heat transfer area to net power output (A/W-net), and electricity production cost (Epc), have also been analyzed and optimized. Results show that R141b, R123 and R245fa present the highest eta(th) and P-net values ranging from 16.60% to 13.30% (eta(th) value), and from 60 to 49 kJ/kg (P-net value). Meanwhile, the three fluids also express the lowest Epc values ranging from 0.30 to 0.35$/kWh, and lowest A/W-net values ranging from 0.436 to 0.516 m(2)/kW. The optimum evaporating pressures for R141b, R123, R245fa are ranging from 2.8 MPa to 3.6 MPa. Research Subject: Waste heat recovery technology in internal combustion engine: The key technology on the improvement of ICE efficiency. (C) 2012 Elsevier Ltd. All rights reserved.