Abstract: In this paper, varieous conditions,suitable for determining ultratracea-mounts of Cu²⁺ when mixed reductant of sulphanilic acid and α-naphthyl-amine is oxidized by H₂O₂ using as a catalytic reaction,have been examined in detail. The sensitivity of this method presented as apparent molar absorptivity equals 1.25×10⁷. The interference of many common ions can be separated by precipitating with ammonia. Trace amounts of Cu²⁺ in some high-purity reagents, such as NaCl, LiCl·H₂O, were determined by this method with satisfactory results.