Slabs are one of the most important structural elements. The main function of the slab is to resist the loads coming normal to its plane. In general practise, the load transferred from slab to beam is taken in the analysis without considering slab stiffness. In present work a G+4 L shaped building frame is analysed with and without consideration of slab stiffness by using STAAD.Pro software for gravity and seismic loads. Frame forces, nodal displacements and support reactions are compared to evaluate the effect of slab stiffness. The results indicate that there is a significant reduction in shear force, bending moment of the beam members and displacement of the roof nodes due to consideration of slab stiffness. Its effect on vertical support reaction is found to be insignificant, however considerable reduction is observed in case torsional and bending moment at supports. The slab stiffness causes redistribution of axial force and bending moment in columns whereas significant reduction is observed in case of torsional moment in columns. In present work approximately 15% lesser steel is required when stiffness of slab is considered in the analysis resulting in an economical design.