The performance of organic Rankine cycle was numerically investigated to recover heat from the exhaust of a heavy-duty diesel engine. Exhaust flow rates and temperatures are obtained from the simulation of diesel cycle by using GT-Power. The net power outputs of organic Rankine cycle for 9 working fluids were calculated by cycle simulations. The results showed that as for the net power outputs and the pressure of working fluids, R21 and R245fa are suitable as working fluids for ORC in diesel engine.