This investigation deals with the experimental evaluation of the performance of carbon fiber composites used for flexural strengthening of six reinforced concrete beams. The experimental program consists on the tests of seven simply supported beams with an overhanging portion, each one with the same cross section, steel reinforcement and span.The beams were designed to have the same value of maximum positive and negative moments. The first beam was not strengthened and it was used as a reference beam. The flexural strengthening of two categories of beams was considered. Category I beams were designed with equal flexural strengthening in the maximum negative and positive moments region. Category II beams were designed with double flexural strengthening in the maximum negative moment region.A total of three concrete beams of each category were constructed, instrumented and tested at the PUC-Rios Structures and Materials Laboratory. The average concrete strength was 20 MPa. The reinforcement steel bars have a yield strength of MPa. The flexural strengthening was applied under loading.The responses of the beams in terms of deflections, strains and modes of failure were examined. It was possible to verify a significant increasing in loading-carrying capacity of the beams due to strengthening. The results of this investigation are useful in substantiating the design data and providing design guidelines for this type of strengthening and they show that the energetic criterions are adequate parameters for the analysis of the beams.