Abstract: Remarkable catalytic effect on the oxidative decoloration reaction between potassium bromate and bromocresol purple by the presence of traces of Ce(Ⅳ) was observed in an ammoniacal buffer solution of pH 9.0.Based on this fact,trace amounts of cerium(Ⅳ) were determined photometrically be measuring the difference in absorbance (ΔA) of the testing solutions in the presence and absence of Ce(Ⅳ) at the wavelength of 580 nm.Linear relationship between ΔA and concentration of Ce(Ⅳ) was found in the range from 0 to 4.0 μg of Ce(Ⅳ) per liter of solution,with a detection limit of 0.092 μg·L-1.In its application to the analysis of samples of human hair,tea and rice,RSD′s found were in the range of 3.6%-5.4%,and recoveries obtained were in the range of 96%-103%.