This research introduces the real behaviour of R.C two-way slab with additional top and bottom corner reinforcement. Such reinforcement contributes in stiffening slabs corner to resist torsional and shear stresses. For this purpose a numerical studies have been performed to illustrate the effect of such reinforcement on the structural behaviour of R.C slabs .the 3D-FEM model through (ANSYS) software package has been used to accomplish this study, the eight node solid element is used to model the concrete, this element is capable of having plastic deformation, cracking in three orthogonal directions, and crushing which were all taken into consideration. The reinforcement was modelled as a three–dimensional bar element. In this research several parameters have been taken into consideration :(a)percentage of slab main reinforcement;( b) percentage of corner reinforcement as a ratio from the main reinforcement ;(c) corner reinforcement spacing;(d)margin beam stiffness ;(e)slab rectangularity. The results show that the existence of corner reinforcement in R.C two-way slabs improves considerably the structural behaviour of such slabs leading to higher ultimate load and lower values for deflection. In this research the maximum midspan deflection and the ultimate load carrying capacity were recorded. It has been found for the studied cases that the increase of load carrying capacity is up to (28%) and the decrease in central deflection of slab is up to (30%). From this study it can be found that the distribution of corner reinforcement (S=7, 14,21cm) and its percentage from the main steel (43%, 72%, 100%) has a significant effect on increasing ultimate load and decreasing the central deflection