Abstarct: In this study, according to the increasing importance of ORC cycles in industries and important role of working fluids on increasing of the efficiency of this cycles, a trying to find the optimal fluid for a cycle with a maximum temperature of 150° C has been carried out. Then those parameters affecting the efficiency and output power of a radial inflow turbine for ORC cycles has been investigated. Finally, with changes in input parameters such as mass flow rate, pressure and temperature tried to examine the impact of these changes on the selected turbine efficiency and output power has been investigated until it’s performance at off-design conditions be specified partly.