A planet gear with thin rim, which has a small radial clearance between the rim and the gear shaft, is chosen as the subject of study. The stress distribution in the planet gear is analyzed by the photoelastic method and the following results are obtained: Fillet stresses are not proportional to the tooth load and they vary with the radial clearance even if the tooth load is constant. Both the position and the magnitude of the maximum stress occurring in the planet gear vary with both the tooth load and the radial clearance. Furthermore if the ratio of the radial clearance to the tooth load is constant, fillet stresses in the planet gear are proportional to either the radial clearance or the tooth load.