The intent of this paper is to study the structural behavior of voided normal and high strength reinforced concrete two-way slabs. Voided slab is a hollow core slab which has an advantage of reducing self-weight by reducing concrete mass within the center zone of the slab section. The experimental program included testing of twelve simply supported slab specimens with dimensions of (1100 x 1100 x 100) mm, and they were subjected to vertical four patch loads. Many parameters were included, such as shape of voids (spherical and cubic), type of concrete strength (normal of 30 MPa strength and high of 60 MPa strength), and ratio of steel reinforcement (0.002, 0.0026). In addition, they have different values of dimension of void to slab thickness (D/H) ratio (0.5, 0.6 and 0.65). The experimental results showed that the use of voided slabs tends to save in self-weight up to 21.6%. The use of spherical voids in voided slabs is more effective than cubic voids due to cracking and ultimate loads capacity and the structural behavior. The use of voided slabs led to reducing the first cracking load in a range of 15%-62% and 5%-40% for high and normal strength, respectively. Also, using voided slabs tended to reduce the ultimate load capacity in a range of 8%-26% for balls and 9%-48% for cubes. Using high strength concrete in voided slabs led to reducing the crack width in a range of 18.2%27.8% for voided slabs (65 mm ball shapes). Decreasing the size of voids led to reducing the deflection for the same stages of load in a range of 20%-35.7% for high strength voided slab (ρ= 0.20% ball shapes) specimens. Increasing the reinforcement ratio from 0.2% to 0.26% led to reducing the deflection in a range of 1.6%-35.9% for high strength voided slab (ball shapes D=60mm) specimens.