This disclosure is to provide a brass-plated steel wire for reinforcing a rubber article, which is capable of improving overvulcanization adhesiveness. This disclosure is a brass-plated steel wire for reinforcing a rubber article, wherein: when measured with XPS (X-ray photoelectron spectroscopy), an outermost surface contains zinc at an amount of 4.93 to 14 atom %, and contains oxygen at an amount of 50 atom % or less; and in the outermost surface, an atomic ratio of copper to zinc is more than 2.33 and 6 or less.