Three brass-plated steel cords with different copper contents from 51.4 to 75.5% were prepared and their adhesion properties to rubber compound were examined. Adhesion properties improved with the decrease in the copper content. The high adhesion of brass-plated steel cord with low copper content to the rubber was obtained after cure and after hostile aging treatments. The stability against humidity aging and the cause for the high adhesion of the brass-plated steel cord with low copper content were discussed in conjunction with the formation and growth of adhesion interphase determined by Auger electron spectroscopy depth profile. The excellent adhesion stability of brass-plated cord with low copper content can be explained by the suppression of the excessive growth of copper sulfide and the inhibition of dezincification due to the low copper content.