Centrifugal pumps performance is highly affected by working fluid viscosity. So, optimization of such pumps for pumping of viscose fluids is very important. In the present paper, multi-objective optimization of the centrifugal pumps is performed to obtain optimum impellers for pumping fluids with various viscosities at different volumetric flow rates. In this way, theoretical head and impeller hydraulic losses are considered as objective functions. Design variables defined in this optimization problem are passage width of impeller and outlet angle of blade. Diagrams of Pareto fronts and Pareto sets are extracted for different viscosities and different volumetric flow rates. Some trade-off optimum design points are selected from all non-dominated points using three different methods namely break point, TOPSIS and near to ideal point. Such methods are defined completely and employed to achieve compromising point successfully. Obtained optimum points contain interesting results which cannot be achieve without using proposed multi-objective optimization approach.