The thesis starts from the need to identify methods, materials and techniques that can contribute to the stregthening of the reinforced concrete structures. Fiber reinforced polymer (FRP) application is a very effective way to repair and strengthen structures that have become structurally inefficient over their life span. CFRP laminates are new carbon-based composite materials that attach externally to concrete beams. These hight strenght materials improve the bending behavior of beams. The main objective of the research, described in this thesis, is the analysis of the response behavior of retrofitted reinforced concrete beams with CFRP laminates. This implied an experimental study, with took place in the Laboratory for Technical Innovation in Structures and Materials (LITEM) of the Department of Strenght of Materials and Structural Engineering of the Polytechnic University of Catalonia. During the experiments, the following aspects were evaluated and recorded regarding the response of the tested beams: load-displacement analysis, deformation behavior, stress distribution, displacement profiles, failure modes and crack patterns. In order to attain these goals, we used five reinforced concrete beams, differently preparated for the test (one control beam, two beams with one CFRP laminate attached and another two beams with a pair of the same laminates). Final observations have confirmed the efficiency of the composite strengthening system. Also we noticed that the results were close to the theoretical values, in most of the aspects.