Fracture behavior and size effect is a major issue in reinforced concrete structures.In this study experimental research was carried out to evaluate the comparative fracture performance of random steel fiber-reinforced composite（SFRC）and aligned steel fiber-reinforced composite（ASFRC）.Experimental results were further analyzed with several fracture mechanics models to see how far the research properties can be enhanced with aligning the steel fiber.The reinforcement can be effectively done by aligning the steel fibers in cementitious composites with use of solenoid magnetic chamber.Thus,the desired direction of steel fiber in the fresh cementitious mortar was achieved by the electromagnetic field.Various dimensions and steel fiber contents by volume Vf were considered to study fracture performance and investigate the size effect.The results from finite specimen sizes were theoretically extrapolated to a higher range.Greater numbers of steel fibers along the crack surface in ASFRC influence the crack growth differently than those of ordinary SFRC and greatly affect the fracture parameters of ASFRC.Therefore the critical fracture parameters in terms of critical crack length were analyzed with theoretical procedure followed by experimental method.The fracture performance was compared for SFRC and ASFRC based on fracture testing of the beams according to the RILEM recommendation.The experimental load-crack mouth opening displacement curves were obtained for every specimen.For the pre-peak region,use was made of fracture toughness while post-peak behavior was analyzed with work of fracture method,which suggests total fracture energy and characteristic length as fracture parameters.To accurately address the ductility of ASFRC,use of conventional method and procedure based on initial compliance were simultaneously applied.The initial cracking parameters are very important for warning and critical analysis are investigated and comprehensively discussed for SFRC and ASFRC,which further enhances our understanding about the improved fracture behavior of ASFRC.The initial cracking load was detected with strain gages to evaluate initial fracture toughness KICini.The fracture parameters were analyzed by nonlinear fracture models,namely the size effect model（SEM）,work of fracture method（WFM）,and double-K fracture criterion（DKFC）.Initial fracture energy,critical fracture toughness Kic,length of fracture process zone,and critical tip opening displacement from SEM,total fracture energy,and characteristic length from WFM was studied for SFRC and ASFRC.Unstable fracture toughness KICun from DKFC with special emphasis on size effect was obtained.SEM was applied to extrapolate the results for infinite size specimen using the results of small range laboratory size specimens.The results show that the rise of specimen depth has no considerable effect on the KICun while the size effect of KICini is not significant.As the increment of Vf,both the KICini and KICun show a linear ascending trend and both of them are greater for ASFRC than that of SFRC specimens.It is found that there exists a strong correlation between the fracture toughness measured by DKFC and SEM（KIC from SEM≌KICun from DKFC）.Generally,the fracture performance of ASFRC relative to that of random SFRC is improved by more than 80%.The difference in fracture performance is obvious for all tested specimens of ASFRC as compared to random SFRC.The fracture properties were improved significantly by alignment of steel fibers.It was observed that the fracture properties of ASFRC specimens with Vf 0.8%are more or equal to that of SFRC with Vf 1.2%and it was revealed that high fracture properties can be obtained at a lesser amount of steel fibers relative to those of ordinary SFRC.