Abstract: The reactivity of reactive dye Doractive WN3BR with the amidogen of chitosan was utilized for determination of chitosan content on cotton fabric.Chitosan finished cotton fabric was dyed,its color yield(K/S value) was measured,and the K/S value was found to have a good linear relationship (R=0.997 3) with the content of chitosan which has been finished on the pure cotton fabric in the range of 0～15 mg/g(cotton fabric).Through measuring the content of nitrogen,the good linear relationship between the chitosan content and the K/S value of the cotton fabric finished with chitosan was proved and the standard working graph was set up.On this basis,a measurement of content of chitosan finished on pure cotton fabric was established by measuring the color yield of dyed cotton.This measurement is simple,fast and less deflective.