The aim of this study was to prepare arsenic trioxide (ATO)-loaded stealth PEGylated PLGA nanoparticles (PEG-PLGA-NPs) and to assess the merits of PEG-PLGA-NPs as drug carriers for ATO delivery. PEG-PLGA copolymer was synthesized with methoxypolyethyleneglycol (Mw=5000),D,L-lactide,and glycolide by the ring-opening polymerization method. Amorphous ATO was transformed into cubic crystal form to increase its solubility in the organic solvent. ATO-loaded PEG-PLGA-NPs were prepared by the modified spontaneous emulsification solvent diffusion (SESD) method,and the main experimental factors influencing the characteristics of nanoparticles were investigated,to optimize the preparation. To confirm the escape of PEG-PLGA-NPs from phagocytosis by phagocytes,PEG-PLGA-NPs labeled rhodamine B uptake by murine peritoneal macrophages (MPM) were analyzed by flow cytometry. The results showed that the physicochemical characteristics of PEG-PLGA-NPs were affected by the type and concentration of the emulsifiers,polymer concentration,and drug concentration. ATO-loaded PEG-PLGA-NPs,with particle size of 120.8nm,zeta potential of -10.73mV,encapsulation efficiency of 73.6%,and drug loading of 1.36%,were prepared under optimal conditions. The images of transmission electron microscopy (TEM) indicated that the optimized nanoparticles were near spherical and without aggregation or adhesion.The release experiments in vitro showed the ATO release from PEG-PLGA-NPs exhibited consequently sustained release for more than 26d,which was in accordance with Higuchi equation. The uptake of PEG-PLGA-NPs by MPM was found to decrease markedly compared to PLGA-NPs. The experimental results showed that PEG-PLGA-NPs were potential nano drug delivery carriers for ATO.