Abstract The influences of the degrees of hydrolyzation and polymerization of poly(vinylalcohol) (PVA) used as an emulsion stabilizer were investigated on the preparation of poly( dl-lactide-co-glycolide) (PLGA) nanoparticles with the spontaneous emulsification solvent diffusion process. The productivity of PLGA nanoparticles and the physical properties, i.e. particle size and redispersibility, of the resultant PLGA nanoparticles varied drastically depending on the PVA grade used. It was found that the degree of hydrolyzation of PVA was more important than the degree of polymerization to improve productivity and physical properties. The use of low-hydrolyzed PVA was useful to attain excellent productivity of PLGA nanoparticles, i.e. higher yield and uniform size distribution of nanoparticles, whereas highly hydrolyzed grade provided poor productivity and unsatisfied properties, e.g. poor redispersibility. A series of gelatinization studies of PVA suggested that the localized gelatinization of PVA preferentially occurred on the surface of emulsion droplets containing PLGA in the solvent diffusion process, thus influencing the formability of PLGA nanoparticles. These results indicate that proper choice of PVA grade was a key factor to determine the preparation behavior of PLGA nanoparticles.