The heat transfer in batch emulsion polymerization of styrene and vinyl acetate has been studied using reaction calorimetry. The effect of the properties of the reaction mixture (monomer to water ratio, polymer to water ratio,type of monomer/polymer used in the system and the conversion from monomer to polymer) as well as the influence of process conditions (impeller speed and impeller type) on the overall and partial heat transfer coefficients inside the vessel have been investigated. The results indicate that both process conditions and system properties such as type of monomer and solids content significantly influence the heat transfer in emulsion polymerization systems.