From the color developing reactions of various phenylenediamine derivatives (I)-(V), oxidizing agent and gold(III). the combination ofN,N-dimethyl-p-phenylenediamine (DPD)(II) and potassium persulfate in acidic media was used for a simple and sensitive spectrophotometric determination of gold(III). The calibration graph was linear in the range of 0–300 ng/10 ml gold(III) with a molar absorptivity of 1.9 × 106l mol−1cm−1at 552 nm. The proposed method had higher sensitivity than other spectrophotometric methods, and was applied to the assay of gold(III) in gold-pharmaceuticals such as sodium aurothimaleate and auranofin. The results were satisfactory.