A numerical model is developed by evolving an efficiency prediction code for the predesign of radial turbines with one sided and two sided that are used in Organic Rankine Cycles. The efficiency prediction code includes the mean-line calculations associated with an optimizer which is based on the multi-objective genetic algorithm embedded in MATLAB. The model is verified with the experimental data existing in the literature for a small size radial turbine using working fluid of Argon. The pre-design studies are extended for the working fluids at high temperature range; Dimethyl Carbonate and n-heptane, at intermediate temperature range; R113, cyclo-pentane and acetone, at low temperature range; R123, iso-pentane, R141b and n-pentane at revolutions of 3000, 6000 and 9000 rpm. The cycle calculations are performed for the organic fluids in the range of real gas condition using a fluid property database, CoolProp. Pareto Diagrams are used to determine the best design revealing the overall picture. Finally, impeller geometry is created using inverse design procedures. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.