An analytical study is presented of the ductile behavior of simply supported, prestressed composite steel beams with a constant eccentric prestressing force applied along the entire span. The stress conditions at the point of maximum moment are presented and the moment angle-change characteristics of the structure are developed for various stages of loading to the ultimate load condition. Comparisons are presented between the moment capacities of the conventional and the prestressed composite beam. The prestressed beam exhibits higher yield and ultimate resistance to applied moment if prestressing is efficiently used. Furthermore, in prestressed construction, more efficient use is made of the concrete slab in carrying its share of the applied load, and higher ultimate moment capacities are obtainable because of the more favorable distribution of the rectangular stress blocks. The yield moment capacities of the prestressed beams were 25% to 35% greater than the yield moment capacities of the conventional composite beams, and the ultimate moment capacities of the prestressed beams were 10% to 20% greater.