The concrete jacket method is a common method used in retrofitting buildings. Although this method has many advantages, engineers criticize it due to an increase in the structure's weight. In the present study, lightweight concretes containing silica nanoparticles (SNPs) and glass fibers (GF) have been used in concrete jackets to strengthen concrete beams. Several reinforced concrete (RC) beams were constructed and retrofitted using the proposed lightweight concrete jackets and their response to fourpoint loading was evaluated. The SNPs amount in the lightweight concrete jackets was 0, 2, 4, and 6% by weight of cement and the amount of GF was 1.5% by volume of concrete. Load-deflection curves were extracted and the response of the beams was examined by parameters such as crack load, yield load, maximum load, energy absorption capacity, and ductility. The proposed lightweight concrete jacket containing 1.5% of GFs in which 0, 2, 4, and 6% of SNPs were used, increased the energy absorption capacity by 33%, 54%, 61%, and 62%, respectively. The presence of SNPs in lightweight concrete reinforced by GFs leads to the filling of small cavities in the concrete. Also, the bearing capacity of the retrofitted RC beams increased with an increase in SNPs in the concrete jacket. A portion of this increase can be attributed to an increase in tensile and compressive strength of the proposed concrete, and the other part can be attributed to the effect of SNPs on the surrounding surfaces of the main beam and jacket.