Abstract: It was reported that in a dil.H2SO4 medium,the redox reaction between eosin Y(abbreviated as ESY) and KBrO3 was sensitized by addition of CPB,and that the same reaction was inhibited by the presence of tannin.Conditions of the reaction were studied and optimized.Kinetic parameters of the reaction were also determined.Based on these facts,a new inhibitory kinetic photometric method was proposed for the determination of trace amounts of tannin in foodstuffs.Values of absorbance were measured at the wavelength of 540 nm.Linear relationship between the magnitude of decrease in absorbance and the concentration of tannin was obtained in the range of 0.02-0.35 mg of tannin per liter,with a detection limit of 0.01 mg·L-1.The proposed method was applied to the determination of tannin in samples of tea and beer,giving values of RSD′s(n=6) in the range of 0.78%-2.36% and values of recovery in the range of 99.6%-101.0%.Mechanism of the inhibitory reaction was also discussed.