The adhesion between a p-hydroxy-benzoic acid (POB) containing rubber compounds and a brass-plated steel cord was investigated to understand the role of POB as an adhesion promoter. The cure rate slowed down when POB was added to the rubber compound, but changes in the physical properties were not significant. An improvement in adhesion was seen with a low loading of POB in the range of 0.5-1 phr, while an adverse effect was observed only with a high loading at 4 phr and a long aging time of 15 days. The adhesion interphase between a rubber compound and a thin brass film studied using AES showed an acceleration of the copper sulfide formation by POB incorporation, resulting in an enhancement of the adhesion. However, a higher POB loading as well as a longer aging time leads to a large increase in the migration of copper into the rubber and excessive growth of the zinc oxide layer, resulting in a decreased adhesion property.