This paper studies a durability of a ultra-micro reduction gear using the mechanical paradox planetary gear mechanism. The module of the gears are 0.1 and the diameter of the unit is 10.6 mm. The gears are made of fiber reinforced PPS (poly phenylene sulfide). Durability tests were carried out using a developed test rig. The wear amount was evaluated using the base tangent length measured by a profile projector. Backlash of the unit was also evaluated. The based tangent length decreased slightly (1% in maximum) in the durability test. The median of the backlash increased slightly (0.1 degrees) after the durability test. Some large backlash values, which are larger than 0.5 degrees, were observed after the durability tests.
