© 2020 Institution of Structural EngineersThe most destructive effects of earthquakes in Turkey are seen in rural areas and slums. Since most of the masonry structures in those areas are not built in accordance with regulations and standards, they are not able to withstand earthquake effects and, eventually collapse. This situation demonstrates the importance of developing effective strenghening techniques for masonry structures. In Turkey, however, scientific studies usually focus on reinforced concrete, steel, and prefabricated structures. Studies on the strengthening of masonry structures, which constitute the majority of the buildings in Turkey, are more limited. Therefore, the shear behaviour of masonry bearing walls must be analyzed to develop appropriate strengthening techniques against potential earthquakes. In this study, walls made of masonry bricks were strengthened by applying lean and steel fibered repair mortar with different thicknesses on both sides. The mortar was applied by plastering the wall surfaces with a trowel. Seven wall specimens were tested diagonally; one was the reference specimen, and six were the reinforced specimens. The results obtained were compared in terms of strength, ductility and energy consumption values.