This paper describes a size-dependent electroless plating method to fabricate a new type of probe with a locally decreasing thickness of metal and a tiny tip size for a combined high resolution shear-force and near-field optical microscope. In this method, the tip size and decreasing thickness profile, which affect the resolution capabilities of the microscopes, are controlled by adding a continuous ultrasonic wave with a frequency of 1MHz to a nickel plating bath. The probe with a tip radius of curvature of 25 nm was successfully fabricated at an ultrasonic power density of 1.6 Wcm_2, its metal thickness gradually decreased from 850 to 20 nm toward the distal tip. #2006 The Optical Society of Japan