Ant colony optimization (ACO), a heuristic method formerly applied on combinatorial problems in the field of applied mathematics and industrial engineering, is described and employed for the multiobjective optimization of hybrid laminates for obtaining minimum weight and cost. The investigated laminate is made of glass-epoxy and graphite-epoxy plies to combine the lightness and economical attributes of the first with the high-stiffness property of the second using the weighting sum method in order to make the trade off with the cost and weight as the objective functions and the first natural frequency as the constraint possible. The results obtained by ACO including the Pareto set, optimum stacking sequences and number of plies made of either glass or graphite fibers are compared with those achieved by the GA reported in literature. The comparison, besides confirming the idea of hybridization, clearly shows that the ACO has outperformed GA or resulted in identical solutions. In the latter case, it seems that both GA and ACO have reached the global optimums.

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