It has already been reported that when nylon (MC nylon) was filled with synthetic wax, the coefficient of friction decreased, and in the case of using such wax-filled nylon for gears, the wear of teeth was reduced, and the amount of gouging of the teeth roots by the top corners of teeth on matching steel gears decreased: accordingly, the change of pressure angle became less. In order to confirm whether phenomena such as these may also occur in polyacetal or not, gears were made with material having a small coefficient of friction by filling polyacetal with fluorine-containing resin, and trial operation was carried out. The wear of teeth, change of teeth profile and other properties were examined, and by comparing them with those in the case of polyacetal gears without filling, the effect of reducing friction was investigated.