Several film-resistor materials and the general requirements for the surface of the substrate are described. The insulation resistance of the substrates at high temperature were measured. The effects of various subsrates upon the load lives of the three kinds of film resistors were investigated. It has been pointed out from the tests of the metal film resistor that the initial changes of the resistance were semi-permanent on D.C. load and the electrochemical corrosion of the films was gradual and relatively long. This effect had much to do with the test conditions and could be slowed down by derating. The different contents of Na+ and k+ in the substrate showed quite different effect.This paper presents some possible methods for improving the D. C. aging performance of film resistors. By comparing the load lives of the newer and older substrates it is considered to be very effective to add alkali-earth metal oxides as the flux for the ceramic substrate.