Abstract: AIM:To establish a reliable method for assay of chitosan.METHODS:Spectrophotometry of a resultant green complex between bromocresol green and chitosan was systemically evaluated for the determination of chitosan.RESULTS:The reaction between bromocresol green and chitosan arrived its end in 5 min at 37 ℃.The formed complex showed maximal absorption wavelength of 620 nm which could remain stable in 2 hours.The assay indicated a linear range up to 10.0 g/L with a correlation coefficient of 0.999 6.Coefficients of variation of the assay at low,middle,and high levels were 0.81%,0.78% and 0.26%,respectively.The averaged recovery was 99.17%.It was also found that the cell wasn′t stained with the pigments and there was no cross-over containment.However,interferences resulted from surfactant,metalion,and albumin.CONCLUSION:This method was reliable,simple,and rapid.It could meet the need of chitosan determination.