Although a thiourea-immobilized polystyrene sorbent has been reported to exhibit high Ag+ sorption capacity (135 mg/g), it is not stable under the acidic conditions commonly employed for desorption. In this research, we synthesized novel thiourea-immobilized polystyrene (TA-PS) nanoparticles to be highly acid resistant via a two-step procedure from polystyrene nanoparticles: acetylation and the subsequent immobilization of thiourea. We investigated the influences of pH, contact time, and initial concentration of AgNO3 solution on the Ag+ sorption of the polymer nanoparticles and estimated the maximum Ag+ sorption capacity to be 190 +/- 5 mg/g at a pH of 6. The sorption performance did not significantly decrease in tap water containing competing ions. The sorption kinetic data were well fitted to the pseudo-second order kinetic model. Overall, the TA-PS nanoparticles exhibited a high Ag+ sorption capacity and high selectivity against alkaline and alkaline earth-metal ions. In particular, their high acid resistance allows them to be used for long time periods in sorption-desorption processes. (C) 2017 Elsevier B.V. All rights reserved.