The separation ability of new UF membranes based on blends of polysulfone (PS) with hydrophilic polymers (HP) was investigated in purification of polymer nanoparticle latices prepared by seeded emulsion polymerization. Low molecular weight components (emulsifier, sails, initiator) used in the synthesis of both glycidyl methacrylate (GMA) and sulfonated (SSS) nanoparticles as well as monomer residues were separated from nanoparticles of colloidal size (70-100 nm) by diafiltration using a three-compartment through-flow cell equipped with two membranes. In contrast to traditional pressure-driven diafiltration, this process is carried out under vacuum. The efficiency of new membranes and some commercial membranes were compared in the purification of nanoparticles. The influence of the nature of HP and structural characteristics of the skin layer of UF PS/HP membranes on their permeability to components of latex emulsions was estimated. The structure parameters of the skin membrane layer varied in the intervals: 1-7 nm (average diameter of pores), 0.6-49.2 x 10(10) (pore density) and 0.1-0.88% (relative surface porosity). For each type of membrane, an optimum correlation between the structure membrane parameters was found for ensuring the maximum permeate flux and purification degree of nanoparticle emulsions. It was shown that 95-98% and 85-89% purification degrees of GMA and SSS nanoparticle emulsions can be achieved by 6 h diafiltration with some UF blend PS/PVP membranes.