Emulsion polymerization of vinyl acetate was investigated in batch and continuous flow operations performed at the same ratio of initiator, emulsifier and monomer concentrations, and at an emulsifier concentration lower than CMC. The batch operation showed a time-independent particle size distribution (PSD) of primary particles smaller than 0.3 mum, which indicated that agglomeration of colloidal polymer particles to produce secondary particles did not occur. The continuous flow operation with separate feeds of monomer and aqueous solution of initiator and emulsifier showed in the first stage (the first 90 min) the same steady-state PSDs as in batch operation, and in the following stage (after 120 min), gave time-dependent PSDs, the median of which shifted gradually from 0.1-0.3 to approximately 1.0 mum over about 3 hours. The oligomer and fine particles continuously generated by homogeneous nucleation were precipitated selectively onto large secondary particles in the second stage of continuous operation. After all secondary particles that had finished growing by selective precipitation had been discharged from the reactor, the same growth process of secondary particles was repeated.