Abstract: Optimum conditions of color reaction of Cu(Ⅱ),Co(Ⅱ) and Ni(Ⅱ) with xylenol orange (XO) in the presence of CTMAB were studied and by using the K-coefficient method,simultaneous spectrophotometric determination of copper,cobalt and nickel in cobalt ores was accomplished.Beer′s law was held in the ranges of 0-800 μg·L-1,0-1.60 mg·L-1 and 0-1.2 mg·L-1 for Cu(Ⅱ),Co(Ⅱ) and Ni(Ⅱ) respectively.The proposed method was applied to the analysis of a cobalt ore sample,giving values of RSD′s (n=5) 3.5% (for Cu),4.9% (for Co) and 3.4% (for Ni),and of average recovery 103.3% (for Cu),92.6% (for Co) and 99.0% (for Ni).