Masonry structures are one of the most vulnerable types of structures in the earthquake due to massive mass and low material resistance. There are many ways to Seismic Rehabilitation of masonry structures, but the existing methods along with the running time, also lead to the difficulty of implementation. Also, the common methods impose a massive mass to the structure, which itself increases the earthquake lateral forces and it will be necessary to strengthen the foundation of the structure. In the recent decades, the use of engineered cementitious composites (ECC) has become commonplace to increase the bearing capacity and ductility in structural members. Composite ECC is High Performance Fiber Reinforced Cementitious Composites (HPFRCC) which due to its high tensile strength and composite strength, it seems that the use of these materials in retrofitting masonry walls, not only can increase the speed and ease of implementation, it also has the capability to confront with other methods in terms of costs. This composite is manufactured with different materials combinations, the components of that can be changed according to the designer's requirements. Usually the main components of the ECC are cement, fly ash, fine grain silica sand and optimal amounts of polyvinyl alcohol fibers (PVA). Due to access restrictions to the fly ash and the cost of silica sand, studies in this research have shown that the use of slag and limestone can be used as a substitute for these two substances in the ECC mixing plan. For this purpose, in the first part of this research, the effect of replacement of different amounts of slag and fly ash with cement, the addition of micro silica and nano -silica, as well as the effect of fiber type and its amount on the strength and toughness of ECC mortar were investigated in 21 different mixing plan. The results of the experiments on the ECC mixing plans show the addition of slag and fly ash increases the ductility of the flexural samples along with reducing the flexural strength. Also, the addition of Micro-Silica and Nano-Silica in the mixing plan compensates the part of the reduction in flexural strength, but it reduces the degree of toughness of the samples. In the second part of this research, ECC mortars have been used to strengthen out of plane of the 7 masonry prisms. The parameters for retrofitting these prisms include the type and thickness of the mortar, the number of reinforced surfaces, the number of galvanized mesh layer in the tensile surface and the length of the PVA in ECC mortar. The results show that the retrofitted an 8 mm thick ECC mortar layer without galvanized mesh can significantly increase the bearing capacity and toughness of the compared to non-reinforced ones. In addition, the increase in the bearing capacity and the toughness of the ECC mortar reinforced specimens with a galvanized mesh layer compared to the reinforced sand-cement mortar with the same specifications is 300 and 400 percent, respectively. Also, the results of the failure of reinforced specimens show that the ECC masonry layer adhesion and the surface of the prism layers are suitably provided, and no proper joints are required to provide the proper performance of the reinforcing mortar. Key words : Cementitous Composites, Flexural Strength, Slag, Toughness Index, Masonry Prism