Biaxial voided slab is an innovative slab system which results in a self-weight reduction of up to 50% in comparison with solid slabs. In this paper, the effect of voids of various shapes on flexural behavior of reinforced concrete (RC) square slabs was studied through experimental investigations. Five full-scale slab specimens under a 16-point load were tested with two different shapes of voids, such as sphere and cuboid. The results obtained for solid and voided slab specimens were compared and found that the ultimate flexural capacity is almost the same. However, the presence of voids influences flexural stiffness. While such influence accounts for a marginal deviation of the post-cracking flexural stiffness, the initial stiffness of solid slabs is observed to be 37% higher than that of voided slabs. Furthermore, the flexural load-carrying capacity was estimated based on the yield line method with tensile membrane action and compared with experimental results. For this, the experimental results of the present study (five specimens) and test data collected from the literature (seven specimens) were compared with predictions. It was found that the beneficial effect of tensile membrane action is applicable for biaxial voided RC slab in enhancing the flexural load-carrying capacity. Furthermore, through the comparison of experimental and analytical results, it is found that the 16-point load can be adopted to simulate uniformly distributed loading condition.