A plasmonic lens composed of a dielectric-filled nanoslits structure on an aluminum film is proposed and experimentally demonstrated. The slits’ structure is designed with equal distance, length, and width, but filled with variant thickness dielectric for specific phase retardations. A dual focused ion beam instrument is employed to mill the slits and deposit into the slits. The phase modulation by -filled slits is illustrated by a double slits interference experiment. The light focusing behavior of the fabricated plasmonic lens is experimentally characterized by a scanning near-field optical microscope. Experimental results show good agreement with the simulations.