Abstract: Fe³⁺ could be restored to Fe²⁺ by tannin in hydrochloric acid medium,and Fe²⁺ reacted with K₃Fe(CN), formed a blue matter which was KFe [Fe(CN)6],the shade of the colour was direct proportion with the amount of tannin in solution.According to these principles,a method for determination tannin in fruit by visible absorptiometry was advanced.The results showed that at pH2.5-3.0 in midium hydrochloric acid,the maximum absorbing wavelength of the matter at 760nm;at this point,the molar absorptivity of the matter was 7.4×10⁵L·mol^-1.cm^-1;and the concentration of tannin in the range of 0.1-1.6μg·ml^-1,com-plied with Beer's law;the rate of recovery of tannin was detween 96.0 and 103.3 percent;the coefficient of variation determined in several parallel tests was 1.6 percent.

Key words: Fruit (Tannin, KFe[Fe(CN)₆], Absorbance, Visible absorptiometry