The aim of this work was to develop a method for optimizing both the design parameters and the mechanical properties of polymer-based nanocomposites using multi-objective optimization (MOO) methods. The objective was to maximize both the elastic modulus and the tensile strength of nanocomposites simultaneously by varying the design parameters. The Ji and Zare models were selected as the objective functions for the elastic modulus and tensile strength of polymer nanocomposites, respectively. For this purpose, the NSGA-II approach implemented in MATLAB was used to obtain optimal solutions of the design variables. The optimization model was able to successfully find optimum solutions of the design variables and the overall optimization results were found to be in good agreement with the available published data. In addition, the proposed optimization model was found to be sufficiently accurate in finding the optimum values of the design variables for improving the mechanical properties of nanocomposites.