We report the synthesis of poly(2-ethyl-2-oxazoline)-based (PEtOx) nanoobjects by polymerization-induced self-assembly (PISA). First, well-defined PEtOx macromolecular chain transfer agents were synthesized by cationic ring-opening polymerization and click chemistry. The photoinitiated PISA of 2-hydroxypropyl methacrylate mediated by these PEtOx produced nanoobjects spanning the full range of core-shell morphologies. The nanoparticles exhibited high biocompatibility and stealth properties in vitro or in vivo, as well as thermoresponsive behavior.