Abstarct: The main objective of this research is to investigate the pull-out behavior of hooked steel fibers and its influence on mechanical properties of fiber reinforced composites. The research is divided into four parts. In the first, mechanical properties of cementitious matrix including compressive strength, tensile splitting strength and flexural strength have been determined. In the second part, pull-out behavior of hooked steel fiber has been evaluated by means of experimental tests on single fiber embedded in cementitious matrix. The pull-out results indicated that the hooked steel fiber exhibits slip-hardening behavior as a result of plastic hinge formation in hooked part of fiber. This mechanism increases bond strength and pull-out energy of fiber. In the third part of this research, pull-out behavior of fiber has been investigated by means of numerical modeling of hooked steel fiber embedded in cementitious matrix. ANSYS software has been used for numerical modeling and obtaining solution. The complexity of numerical modeling arises from nonlinear behavior comprising bond between fiber and matrix in the early stage of pull-out, unilateral contact between fiber and matrix, friction, plastification of steel fiber and cementitious matrix and large displacement and strains during pull-out. All these nonlinearities require special treatment in numerical modeling. The results of numerical modeling were compared and verified with respect to the result of experimental test of hooked steel fibers. The formation of plastic hinge in hooked part has been observed in modeling which results in slip-hardening behavior. Obtained results from modeling were in good agreement with experimental results. In the final part, critical volume fraction of fiber to achieve deflection-hardening behavior has been determined according to pull-out tests results. The critical volume fraction has to be at least 2%. In order to compare different flexural behavior of composites, four- point bending tests performed on cementitious composites reinforced with 1% and 2% hooked steel fibers. The result showed that cementitious composites with 2% hooked steel fibers exhibit defection-hardening behavior as expected. In contrast, specimens with 1% hooked steel fibers showed deflection-softening behavior. Comparing obtained results indicated that deflection hardening behavior will increase flexural strength and have a great influence on toughness and ductility of material.