The inhibition period attributed to ethyl formate in vinyl acetate monomer (VAM) with and without adding hydroquinone (HQ) affected the rate of VAM emulsion polymerization and also the properties of resulting poly (vinyl acetate) (PVAC) emulsion. Ethyl formate (EF) acted as inhibition period enhancer, retarder and chain transfer agent and thus decreased the rate of the emulsion polymerization and reduced the viscosity, solid contents and the particle size of PVAC emulsions.