Ultrasonic waves have been used for improved oil recovery especially from the marginal well in so many areas all over the world.  The main mechanism is to supply oil molecules by energy to overcome capillary forces there by restructuring the relative permeability curves and increasing the oil mobility.  Monitoring these changes is very important for increasing the oil mobility even after residual oil saturation achieved. The present work investigates the laboratory effects of ultrasonic waves on the relative permeability curves. Five sandstone and carbonate cores were used from Egyptian reservoirs. Their permeabilities range from 67 to 460 md. Acoustic ultrasonic waves of 500 KHZ have been applied.  At this frequency, the fluid vibrates out of phase with the solid and is forced out through the pore structure in the agglomerate. This relative fluid motion exerts high viscous stresses at the particle-particle contact points which leads to fracture of the agglomerate and the dispersion of the individual particles. This interaction causes changes in relative permeability of the rock to oil and water. Therefore, the results showed that applying ultrasonic waves has a higher effect in permeability reservoirs (76 md to 460 md) and can mobilize additional quantity of crude oil. The fractional flow curve changes are also addressed and analyzed after wave applications. The aim of this research is to investigate the effect of the ultrasonic wave as a new proposed method to improve oil recovery by changing the relative permeability curves of the reservoirs.