Strengthening of existing Reinforced Concrete structures is becoming a major issue in civil engineering. Externally Bonded Reinforcement (EBR) systems have been successfully applied for strengthening of existing concrete structures. This work includes a results of numerical models carried to investigate the behavior of reinforced concrete, RC, slender columns with rectangular sections under the effect of eccentric loads strengthened with carbon fiber-reinforced polymers (CFRPs) in three different manners in order to enhance its axial and flexural rigidity. The first approach is a well-known form of CFRP strengthening with sheet wrapping columns; the second approach is strengthening using CFRP sheets in longitudinal direction of columns, and a third one is a new retrofitting method of near surface mounted (NSM) CFRP strips. Ten full scale specimens with rectangular cross sections dimensions (210 × 150 mm) were tested under eccentric compressive loading to failure. The total length of all specimens was 3000 mm, with slender ratios 73, 60 and 50 respectively and characteristic strength 25, 35,45Mpa. NSM proved to be very effective in terms of increasing their flexural resistance, as long as the NSM bars can be effectively anchored in the adjacent long columns.