In this paper, the dynamic characteristics of a star type epicyclic gear train have been analyzed. Nonlinear stiffness of a gear pair were obtained considering the bending and shear deformation, Hertz contact deformation, as well as tooth fillet deformation. Nonlinear stiffness coefficients and damping coefficients around the static equilibrium position were obtained by perturbation method. The loci of the planet gears and sun gear were estimated. Tooth meshing forces and bearing reaction forces were calculated. The effects of bearing clearance and oil viscosity on the gear behavior were also analyzed.