To reveal whether organic mixtures perform better in the aspect of matching two heat sources of different grades, this paper presents a dual-loop system for waste heat recovery from internal combustion engine which has two heat sources of different temperature. The high temperature loop with water as working fluid is employed to recover waste heat from engine exhaust gas. And in the low temperature loop, organic mixtures RC318/121234yf, butane/R1234yf and RC318/R245fa are selected as working fluids to recover the heat from jacket cooling water and heat released from condensation process in the high temperature loop. The organic mixtures in the low temperature loop present a better system performance than pure working fluids because of better temperature matching in condensation and better matching two heat sources of different grades. The influence of high temperature loop condensing temperature on the whole system is also analyzed in this research. The simulation results reveal that the appropriate mixture does not only improve the thermal efficiency but also the absorbed heat from heat sources in the low temperature loop. With RC318/R1234yf as working fluid in the low temperature loop, the engine output can be improved by nearly 14.4%. (C) 2016 Elsevier Ltd. All rights reserved.