This paper deals with the optimal design of a flexible planar parallel robot based on kinematic and dynamic criteria simultaneously. The complete kinematic and dynamic model permits to establish the workspace size and the elasto-dynamic performance, respectively. Consequently, the optimal design consists in a multi-objective optimization that is solved by using the multi-objective genetic algorithm. The optimization results permit to find the set of optimal solutions denominated as the Pareto front. These results are analyzed to determine the most suitable solution depending on the desired application.