This study attempts to understand the shear behaviour of externally pre-stressed R.C beams using NSM pre-stressed bars.Nine reinforced concrete beams of cross-section 150 mm width, 300 mm overall thickness and 1400 mm total length were fabricated and tested under three point loads. One of these was fabricated without strengthening while the others were strengthened to study different parameters; damage levels, pre-stressing levels, and spacing of NSM pre-stressed bars. The results showed that the effectiveness of the proposed technique is achieved in both ultimate and serviceability limit state. NSM pre-stressed bars could reduce the effect of the existing cracks and increase the beams capacities. Also, the mode of failure of the strengthened beam changed from brittle failure to ductile failure.