Abstract: Oxidation of Cr(Ⅲ) to Cr(Ⅵ) is the most common method to determine trace Cr(Ⅲ) in water by diphenylcarbohy- drazide spectrophotometric method.The key of this method is not only the convenience and expedition of the totally conver- sion of Cr(Ⅲ) to Cr(Ⅵ)，but also avoids the disturbance of the reaction between the oxidizing agent and chromogenic agent. The methods reported in literature were compared with experiments and some procedures were optimized.Results showed that KMnO4，（NH4）2S2O8，and H2O2 were all good candidates to oxidize Cr（Ⅲ） for spectrophotometric measurement.On contrary， perchloric acid and bromine got unsatisfactory effect.From the viewpoints of accuracy，convenience and safety，persulfate and hydrogen peroxide are the best oxidants for trace Cr（Ⅲ） determination in water by spectrophotometry.

Key words: chromium, spectrophotometry, oxidation