This paper presents selected results of research on the behaviour of an RC beam strengthened with composite materials (CFRPs). The designed tests were to provide data for an assessment of such reinforcement system's performance under cyclically variable loads. The test plan included the effect of the CFRP reinforcement on: beam rigidity, cracking morphology and the interaction of the reinforcement components with regard to bond uniformity in the whole structure and the durability of the bond under cyclic loads. The tests were carried out on two RC beams with the same dimensions, reinforcement and material quality. Only one of the beams was strengthened with CFRP, but both were subjected to the same loading and the same quantities were measured. This facilitated a quantitative and qualitative assessment of the performance of the CFRP reinforcement system. The research was carried out as part of project “Theoretical and experimental investigations of load-bearing capacity and service limit states of reinforced concrete and prestressed concrete structures” (also to be used for educational purposes) in the Accredited Laboratory of the Institute of Building Engineering at Wrocław University of Technology.