The Rankine cycle power system is a promising technology to convert the wasted thermal energy from engines into useful energy. In a way to decrease the CO¬¬2 emissions of passenger cars, it is possible to recover the waste heat from the exhaust gas that presents a high exergy compared to other sources of waste heat (cooling engine, exhaust gas recovery, etc.). A Rankine test-rig is designed and built to assess the performance of such a cycle in real operating conditions. The most critical component is the expander. This component needs to be compact, light, efficient, reliable and cheap among others. In this context, a 1.5 kW axial turbine composed of two wheels is tested on a Rankine cycle test-rig coupled with a 150 kW engine. A detailed analysis of the performance is proposed. The maximum mechanical isentropic efficiency reached is 41.5%. A semi-empirical approach is proposed to predict the performance of the axial turbine in a wide range of conditions. Finally, the performance on a driving cycle is compared with another technology of expander (scroll).