A structural optimization procedure utilizing ant colony optimization (ACO) technique is proposed for design optimization of truss structures. Total weight of structure to be minimized is considered as the objective function and the allowable stress and displacement are adopted as constraints. The truss design problem is transformed into a modified traveling salesman problem (TSP). Therefore, the network of the TSP reflects the structural topology and total length of the TSP tour is considered as the weight of the structure. The present ACO-based design optimization procedure uses discrete design variables and introduces a penalty function to enforce design constraints. Finally, two numerical examples are carried out to show the capability of ACO in truss optimization. From numerical results, ACO can provide a simple but very effective way of finding optimum design of truss structures. Finally, we provide the present numerical results as benchmark test suite for the future reference solution of truss optimization.