In the present paper a model equation for calculating the radical desorption rate constant, k(0), in the emulsion polymerization of vinyl acetate was suggested and the various parameters for evaluating k(0) were determined. Effects of reaction temperature, emulsifier concentration, initiator concentration, monomer conversion and phase ratio on k(0) were studied. It indicates that the desorption of radicals from latex particles to aqueous phase must be taken into account in the modelling of emulsion polymerization for the monomers with higher hydrophilicity such as vinyl acetate.