This paper presents experimental and theoretical investigations on flexural CFRP strengthening/repairing of pretested (i.e., damaged) beams reinforced using prestress rebars. Six beams were fabricated and tested under a four-point bending system to failure. The internal longitudinal tensile and transverse steel reinforcements of these beams were reinforced using prestress and mild steel rebars, respectively. After the application of load, these pretested (i.e. damaged) beams were repaired and tested using externally bonded Carbon Fibre Reinforced Polymer (CFRP) reinforcement. This study investigated the effects of number of CFRP plies, three different grades of concrete, and wrapping layouts. The results confirm that the CFRP repaired beams reinforced with prestress rebars efficiently increased the flexural capacity, however the trend of ductility was inadequate as in damaged-unstrengthened beams. Experimental results show that the flexural capacity of the repaired beams increased to a maximum enhancement of 172.4% over the damaged-unstrengthened beam. It was experimentally observed that CFRP repaired beams with low grade of concrete could provide better performanceas compared to higher grades of concrete. The comparison of experimental and theoretical results had good agreement for higher grades of concrete, whereas, in case of low grade concrete, the experimental results were relatively greater than the theoretical results. © The Author(s) 2011.