This study deals with an ultrasonic oscillation method for friction reduction and lubricity improvement in meshed gears. In recent years, the gear is used in critical environments such as in a vacuum chamber or space environment. Thus, instead of using a conventional method, i.e., lubricant oil, a new method of the friction reduction and lubricity improvement is rather demanding. This paper describes frictional experiments for meshed gears oscillated by an ultrasonic actuator which is fixed on the end surface of the gear shaft. Strain gauges are attached on the fillet between the dedendum flank and the bottomland to measure stress conditions during forward and reverse rotations when a constant torque was applied about the gear axis. The friction on the tooth flank is evaluated from the averaged stress difference between the forward and reverse rotations. The study showed that when no lubricant was applied, the ultrasonic oscillation has reduced the friction between tooth flanks by approximately 40% compared to non-oscillation results.