Prestressed concrete and steel concrete composite are commonly used for constructing bridges. Construction of prestressed concrete bridge is time taking and less reliable. Steel concrete composite bridges have problem of excessive deflection under dead and super imposed loads, live load and deflection due to shrinkage and creep of deck slab concrete. External post-tensioning for strengthening of existing bridges has been used in many countries and has been found to provide an efficient and economic solution for a wide range of bridge types and conditions. External prestressing is now being used for construction of new bridges also. The paper introduces a new concept of prestressed steel-concrete composite bridge, in which external post-tensioning is used in the steel-concrete composite bridge. In the prestressed steel-concrete composite bridge, high tensile wires are tensioned by means of jacks bearing on the end block of the concrete deck slab and anchored. As a result, longitudinal stress level of the concrete deck slab is raised, which not only eliminates shrinkage and creep strains but also improves its fatigue performance. 40.0m and 72.0m spans, un-supported and supported during construction composite and prestressed composite bridges have been considered for the comparison. It is concluded that prestressing not only raises stress level of the deck slab concrete improving its fatigue performance, but it also improves strength and stiffness of the bridge considerably. Further, it is concluded that prestressed steel-concrete composite bridges need not be supported during construction as the deflections under dead load and imposed load are eliminated using prestress. This is highly desirable for longer spans. For example, prestressed steel-concrete composite bridges can be used for longer span up to 80m in comparison to prestressed concrete bridges and steel concrete composite bridges, which can be constructed up to 40m span only.