Abstract: In a nitric acid medium of ca.1.3 mol·L-1,chloride ion in sample solution of boric acid was reacted with silver nitrate to form a colloidal suspension of silver chloride,which was stabilized by adding an appropriate amount of 1,2,3-propantriol (also named popularly as glycerol).Absorbance of the colloidal suspension was measured at the wavelength of 400 nm.Linear relationship between values of absorbance and concentration of Cl--ion was obtained in the range of 0.017- 0.20 mg·L-1.Detection limit (3S/b) of the method was found to be 0.016 mg·L-1.Variou influential factors of the reaction (including wavelength of measurement,acidity of test solution,amounts of silver nitrate solution and 1,2,3 propanetriol required,temperature and time suitable for the reaction,and time at which to make the measurements) were studied and optimized.Recovery and precision were tested,giving values of recovery in the range of 96.0%-102.6%,and values of RSD′s (n=5) less than 2%.