Abstract: It was found that the absorbance of the blue-purple complex formed by tribromoarsenazo (AsA-TB) and zirconium(Ⅳ) in 0.20 mol·L-1 HCl medium was increased upon the addition of definite amount of oxalic acid as measured at 506 nm.An equivalent amount of AsA-TB was displaced from the Zr(Ⅳ)-AsA-TB complex by oxalic acid in forming a more stable and colorless complex between Zr(Ⅳ) and oxalic acid,and the absorbance of the test solution was increased due to the increase in concentration of free AsA-TB,which was liberated in the displacement reaction.Beer′s law was kept in the range of 1.0×10-4 to 6.5×10-4mol·L-1.Molar absorptivity of this method was found as 1.23×103L·mol-1·cm-1.Detection limit found was 0.074 mg·L-1.The proposed method has been applied to the determination of oxalic acid in tomato and ground water,giving results in conformity with the results obtained by the method given in literature.Values of RSD′s (n=13) obtained were less than 2%,and values of recovery were in the range of 95.7% to 103.9%.