The air conditioner installation in general, the air compressor is installed at the external of the building that has well for heat rejected and pretty location. The air compressor must be used the supporting leg for support the its weight. Now a day, the production of supporting leg has the measure to reduce its cost by reduction of material weight but its strength usable. According to material weight reduction, supporting leg shape and cross section may be change. This is the point of this work. The objective work is minimizing the material weight but it also supportable its weight. This problem can solve by the optimization technique. The optimization technique which this way is known and the most widely used for structural design problem is Genetic Algorithms. This research used the Non Dominated Sorting Genetic Algorithms method for solve the multi-objective problem which it are minimize cross sectional area and minimize deflection of supporting leg and the constraint conditions is the supporting leg's bending stress does not exceed the strength of materials.