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Eight slabs with two different longitudinal reinforcement ratios and varying steel fiber ratios were tested  Steel fibers increased the ultimate load capacity for all slabs  Contribution of steel fibers to the displacement capacity was more significant for slabs with higher longitudinal reinforcement ratio Addition of steel fibers in concrete mixture is known to increase the punching resistance of slabs. There are numerous studies, both analytical and experimental, in the literature investigating the effects of steel fibers on the punching behavior of steel fiber reinforced concrete slabs. Figure A. Load-displacement curves for slabs Purpose: This study is concentrates on the effects of steel fibers on the punching behavior of reinforced concrete slabs with different longitudinal reinforcement ratios. Experimental studies on the subject were usually performed with either no or constant longitudinal reinforcement. This study aims to investigate the coupling effects of steel fibers with varying longitudinal reinforcement ratios. Theory and Methods: Reinforced concrete slabs in two groups, having 0.004 (D1 series) and 0.002 (D2 series) longitudinal reinforcement ratios in two orthogonal directions, were cast with concrete mixes containing 0%, 0.5%, 1% and 1.5% steel fiber ratios in volume. Slabs were 2150x2150x150 mm in dimensions. Eight slabs were tested in total under static loads applied at their midpoints. An analytical study of the test specimens were also performed using Critical Shear Crack Theory and based on comparisons of experimental and analytical results some improvements in the model were proposed. Results: For slabs without steel fibers, the slab with higher reinforcement ratio showed punching failure before the yielding of longitudinal bars, whereas the slab with lower reinforcement ratio displayed a significantly higher ductility before final punching failure. Addition of steel fibers increased the punching load capacity up to two times. However, although addition of steel fibers also increased the maximum displacements in D1 series slabs, it did not make any significant effect on the maximum displacements of D2 series slabs. Maximum displacements were still controlled by the yielding of longitudinal reinforcement. Increasing the steel fiber ratio increased both the punching capacity and the maximum displacements in D1 series slabs, but it did not make a significant difference in behavior of D2 series beyond 1% fiber ratio (Figure A). Conclusion: Role of steel fibers on the behavior of slabs is dependent on the longitudinal reinforcement ratio. For slabs with low reinforcement ratio, steel fibers increase the load capacity but do not have a significant effect on the displacement capacity since displacement capacity is still controlled by the yielding of the longitudinal reinforcements. For slabs with high reinforcement ratio, which do not show yielding before punching, steel fibers increase both punching capacity and displacement capacity. Increased punching capacity in these slabs allows yielding...