A new process for improving the fatigue strength of carburized steel gears has been developed, and the effect of the process has been examined with fatigue tests of notched specimens and helical gears for use as automotive transmissions. This process consists of two kinds of treatment: shot peening and chemical polishing. Shot peening yields a highly compressive residual stress near the surface of a workpiece, and chemical polishing removes the oxidized and nonmartensitic layer which is harmful to the fatigue strength. Since the chemical polishing is conducted only by immersing workpieces in a solution containing 1 mol/ℓ of HF and 2 mol/ℓof H₂O₂, it is easy to treat complex-shaped workpieces like gears. Furthermore, a smooth surface and highly compressive residual stress are obtained by treat workpieces with chemical polishing after shot peening. The factors of increase of fatigue strength by means of the combined process are 1.76, 1.63 and 1.51 for the carburized notched specimens whose notch radii are 0.5 mm, 1.0 mm and 2.0 mm, respectively, and the factors of increase of tooth-root fatigue strength range between 1.47 and 1.63 for three kinds of helical gears whose the modules vary from 1.75 to 2.80.