A resistance heating process of a side wall for warm and hot spline forming of cups was developed to manufacture high tensile strength steel gears. The side wall of the cup was heated by the electrification to decrease the forming load and to increase the formability. Since the cross-sectional area of the side wall having a uniform wall thickness is uniform, the heating of the side wall by the resistance heating becomes uniform. The inhomogeneous contact between the electrode and side wall was improved by inserting copper foils in the interface, and thus the temperature distribution in the hoop direction became uniform. The uniformity of the temperature distribution in the axial direction was improved by decreasing the total area of the contact between the electrode and side wall and by increasing the number of contacts. The side wall of the cup was successfully shaped into a gear by the warm and hot spline forming process using resistance heating.