The purpose of this study is to evaluate the effect of natural fibers: sisal and palm fibers on the different properties of concrete have been investigated through a number of tests. The properties investigated include compressive strength, flexural strength, splitting tensile strength and impact resistance of concrete. Sisal fiber has been used at three percentages of total mixture volume (0.6, 1.20 and 1.8%, respectively), while the palm fiber has been added in (2.5, 5.0 and 7.5%,

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... ) by volume. The results of this study show that the concrete is reinforced with sisal and palm fibers improvement in flexural strength and in splitting tensile strength while no significant alteration in the compressive strength has occurred. The results also show improvements in the impact resistance of concrete by the addition of sisal and palm fibers which give maximum increase 114.3 and 285.7%, respectively for 1.8% sisal fiber and 7.5% palm fiber, respectively. The addition of sisal and palm fibres to the plain precast concrete slabs enhances the impact resistance and compensates for the decrease in depth for (500×500×40 mm). The important visual observation is that the predominant mode of failure in all fibers which has reinforced concrete slabs is fiber pull-out. Besides, it has been figured out that the slabs remain together in one piece. They are broken; though. The plain concrete slabs have been totally disintegrated and shattered.