The effect of resorcinol formaldehyde (RF) resin on the stability of the adhesion interphase between rubber compounds containing different amounts of RF resin and the thin brass film deposited on a glass plate was investigated under the conditions of humidity aging. The depth profiles of the adhesion interphase were examined by AES (Auger electron spectroscopy). In the unaged state, there was no significant difference in the adhesion interphase with varying content of RF resin, but the migration of copper and zinc to the bulk of the rubber during humidity aging was considerably suppressed with high levels of RF resin in the rubber compound. The pull-out force and rubber coverage of TCAT (tire cord adhesion test) samples also showed an improvement in the adhesion durability to humidity aging, caused by the addition of RF resin. The improvement in the adhesion stability to humidity aging obtained by adding RF resin to the rubber compound can be explained by a barrier formation effect, which prevents further migration of reactive materials inducing the degradation of the adhesion interphase.