Abstract: In preparing copolymer with homogeneous composition by batch process in two-component copolymerization reaction it is necessary to keep the monomer ratio constant by replenishing the fraction of the more reactive monomer.In this paper a calculation method for monomer feeding is derived, which is capable of controlling the composition of cooligomer during the course of reaction.Some cooligomers of acryloni-trile and butadiene with comparatively homogeneous compositions have been preparedusing this replenishing method. The method would be useful for other two-component copolymerization process.