Abstract: A new method of determination of epoxy value in aqueous solution was proposed based on the acidimetric titration of sodium hydroxide produced by the reaction with sodium sulfite.A definite amount of epichlorohydrin,used as object in the research,was taken and reacted with 1 mol·L-1 Na2SO3 solution in an aqueous medium of definite volume.After a period of 1-2 h,an aliquot of the reaction solution was taken and titrated with standard hydrochloric acid solution.Epoxy value was calculated stoichiometrically according to the formula given in the paper.Effects of time and temperature of the reaction,as well as the pH value of the reaction solution on the determination of epoxy value were studied.Detection limit of the method was found to be 4.5×10-5mol·L-1.Precision and recovery were tested,and values of RSD′s (n=7) and recovery obtained were in the ranges of 1.3%-1.8% and 95.9%-98.6% respectively.