This study presents a new ultrafiltration process using amphiphilic polymer nanoparticles. Unlike micelle-enhanced ultrafiltration (MEUF) using surfactant molecules as nano-absorbent for pollutants, our ultrafiltration process employs amphiphilic polyurethane (APU) nanoparticles as a new nano-absorbent for absorbing pollutants in aqueous phase. APU nanoparticles, dispersed in water, have polypropylene oxide-based hydrophobic interior and polyethylene oxide-based hydrophilic exterior, and the same kind of interfacial activity and solubilization performance of surfactants. Ultrafiltration was carried out using dead-end batch cell equipped with the mixed cellulose esters (MCE) ultrafiltration flat membrane (pore size = 0.025 mm). Under the same UF condition, rejection of APU nanoparticles (greater than 95%) was much higher than that of nonionic surfactant, Triton X-100 (lower than 50%). For removal of various organic pollutants (toluene, benzene, 4-nitrophenol, and phenol) from aqueous phase, rejection of organic pollutants varied from 48 to 97% depending on the nature of pollutant. Removal of metal ions (Cs+, Cu2+, Cr3+, Mg2+, and Ni2+) was also examined via UF at various concentrations of APU nanoparticles. Rejection of metal ions was varied from 20 to 95%. The maximum rejection of metal ions could be obtained for Cr3+ (91.4%) and Mg2+ (95%) ions.