In this paper, twelve strengthened, and one un-strengthened reinforced concrete (RC) beams were experimentally and numerically investigated in flexure. The strengthened RC beams were upgraded with steel or glass fiber reinforced polymer (GFRP) in the form of side-near surface mounted (SNSM) reinforcement. The tested parameters were the SNSM bar diameter, adhesive materials, SNSM end conditions, and materials of strengthening bars. The three-dimensional elastic-plastic finite element program (ABAQUS) was utilized to simulate numerically the tested beams in the experimental program. Finally, a parametric study was numerically conducted to show the effect of different parameters of the SNSM technique on the flexural response of the strengthened beams. The experimental findings demonstrated that the RC beams strengthened with SNSM steel bars generally had higher load capacity than those strengthened with GFRP. Bent ends of the SNSM steel bars were more efficient than in SNSM GFRP bars or end anchorage by GFRP sheets. The load-carrying capacity enhancement for strengthened beams with SNSM steel bars (10 and 12 mm in diameter) having end anchorage (wrapped by CFRP sheets) was 212.6% and 234.7% compared to the unstrengthened beam. In contrast, the enhancement decreased from 184.5 to 145% and 160.5 to 158.3% as the bond material changed from epoxy to grout for the beams strengthened by 10 mm and 12 mm diameters of SNSM steel bars, respectively. The numerical and experimental findings were in close agreement.