To propose a means for treating brass-plated steel wires for the purpose of improving lubricity between a cord and rubber during tire production.

An aqueous suspension containing at least one type of compound such as cobalt and/or nickel salt or cobalt and/or nickel boroacylate (iii) of saturated or unsaturated carboxylic acid (i) or phosphate ester (ii) and at least one type of nonionic or anionic surfactant, wherein the weight ratio of compounds (i), (ii), and/or (iii) to the surfactant ranges from 0.5 to 10. The aqueous suspension is used as a lubricant for the brass-plated steel wire drawing.