The article describes an experiment aimed at developing a method for quantitative determination of maleic anhydride in a terpolymer of ethylene, vinyl acetate and maleic anhydride. The method consists of two stages: separation of free maleic anhydride from the terpolymer, and direct determination of the amount of maleic anhydride in the copolymer. The first stage is carried out by dissolving in o-xylene with subsequent precipitation of the copolymer with acetone. Due to the good solubility of maleic anhydride in acetone and the insolubility of the copolymer, free maleic anhydride is separated from the copolymer. The second stage is based on the reaction of anhydride groups of the copolymer dissolved in an organic solvent with potassium hydroxide until the acid-base reaction of the solution is neutral. The following solvents were selected: o-xylene for the copolymer and propanol-2 for potassium hydroxide. It has been established that no precipitation of the copolymer is observed during titration of the copolymer solution in o-xylene with a solution of potassium hydroxide in propanol-2. Temperature and time conditions of titration for the copolymer have been selected. It has been shown that under these conditions the side reaction of vinyl acetate saponification in the copolymer with potassium hydroxide proceeds significantly slower than the reaction of interaction of anhydride groups with potassium hydroxide. This makes it possible to use the reaction of neutralization of the anhydride with alkali for the quantitative determination of maleic anhydride in the ternary copolymer of ethylene, vinyl acetate and maleic anhydride. To monitor the completion of the neutralization reaction, a color indicator of acidity, thymol blue, has been selected, which adequately reflects the acidity of the solution in an organic solvent. The technique is suitable for both copolymers obtained by direct copolymerization of three monomers and by grafting maleic anhydride to the copolymer of ethylene with vinyl acetate.