Abstract: In order to raise their sensitivity and increa sing their solubility, about 40 thiazolylazo dye have been synthesized and used for many purposes,　e.g.,　as the indicator for the titration of metal ions with EDTA and as chelating agent of metal ions. The article introduces the color reaction of th e new formed developer with the copper(Ⅱ) under the existence of CPB, it was found th at in a buffer solution of pH=6.98. Cu²⁺　reacts with the develop er to form a stable red coordinated complex. Its max-absorption-wavelength is 533.0 nm,　appar ent mol ar absorption coefficient is 3.64　×10⁴　L·mol^-1·cm-1.　Beer's law is obeyed in th e range of 0.001　4~1.2　μg/mL for Cu(Ⅱ). The new reaction system rem ains to have a high sensitivity and a good selectivity. The method proves to be satisfactory for the direct determination of copper in practical samples.

Key words: ３-(benzothiazofeazo)-5-bromo-2,6-bihydroxy benzoic acid, copper, color reaction