Abstract: It was found that in a borate buffer of pH 9.8 and in the presence of Triton X-100,a coordination complex of tin(Ⅱ) and 2-(p-phenylazobenzene)-triazene-benzoic acid (PABTB) was formed with molar ratio of 1 to 2 and having its absorption maximum at the wavelength of 318 nm.Molar absorptivity found at 318 nm was 2.33×105L·mol-1·cm-1.Linear relationship was kept in the range within 15.0 mg·L-1 of Sn(Ⅱ).Based on these facts,the proposed method was applied to the determination of tin in pure copper,giving results in consistency with the results found by the phenyl-fluorone-photometric method,with values of RSD′s (n=5) less than 0.8%.