Abstract: In a B-R buffer medium of pH 4.1,an ion-association complex was formed between kanamycin and azo blue,leading to a color-fading of azo blue,or in other words,a decrease of absorbance of azo blue at its absorption maxima 552 nm.Under the optimum reaction conditions,linear relationship between the magnitude of color-fading intensity and concentration of kanamycin was found in the range of 0.1-4.0 mg·L-1,with value of molar absorptivity (ε522) to be 7.3×104L·mol-1·cm-1 and detection limit (3σ) to be 7.6×10-2mg·L-1.In application of the proposed method to the determination of kanamycin in 2 samples of kanamycin sulfate injection,average values of RSD (n=7) and recovery obtained were 1.1% and 96.5% respectively.