Fatigue strengthening of existing steel structures is of great importance and has attracted lots of interest recently. Apart from the conventional strengthening technique, i.e. utilizing bulky and heavy steel plates and its disadvantages, carbon fiber reinforced polymer (CFRP) composites have exhibited a great potential to be used as external reinforcements in strengthening of steel structures. As a result, during the last two decades, considerable research studies have been done to further investigate static and fatigue behavior of CFRP-strengthened steel members under different loading configurations. Nevertheless, very limited investigations can be found in the literature on the performance of prestressed CFRP plates for fatigue strengthening of cracked steel members; while, it is obvious that using prestressed reinforcements is more effective than non-prestressed ones. Consequently, the main intention of the current study is to show the capability of fatigue crack arrest in steel plates using a novel prestressed unbonded reinforcement (PUR) system, including high performance mechanical clamps. This paper presents a set of fatigue tests on precracked steel plates with and without the PUR strengthening that has been performed. Based on the obtained experimental results it can be concluded that utilizing the proposed PUR system with a certain prestressing level, an existing fatigue crack in a steel member can be completely arrested.