In this paper, the important and useful method for manufacturing superparamagnetic iron oxide nanoparticles stabilized by water-soluble poly(ethylene oxide) (PEO)-based triblock copolymers showing stimuli-responsive phase transition is introduced. Triblock copolymers, such as poly(ethylene oxide-b-N-vinylimidazole-b-3-(methacrylamino)phenylboronic acid) (PEO-b-PVIm-b-PMAPBA), poly(ethylene oxide-b-N-vinylpyrrolidone-b-3-(methacrylamino)phenylboronic acid) (PEO-b-PVP-b-PMAPBA), and poly(ethylene oxide-b-N-vinylimidazole-b-maleic acid) (PEO-b-PVIm-b-PMAc), were synthesized using the sequential monomer addition method via reversible addition fragmentation chain transfer (RAFT) radical block copolymerizations of the corresponding monomers, using PEO-based RAFT agent. After complete polymerization of N-vinylimidazole or N-vinylpyrrolidone in dimethylformamide (DMF) at $110^{circ}C$, 3-(methacrylamino)phenylboronic acid (MAPBA) was polymerized in DMF at $90^{circ}C$ for 24 h, and N-phenylmaleimide was polymerized in dimethylsulfoxide (DMSO) at $110^{circ}C$ for 28 h. All the block copolymers were water-soluble and efficient enough to stabilize the surface of nano-sized iron oxide particles in water. The nanoparticles were stable in neutral aqueous media for at least one month. The resulting products were characterized by a combination of $^1H$ nuclear magnetic resonance spectroscopy (NMR), size exclusion chromatography, transmission electron microscopy (TEM), electron diffraction pattern, and phase transition behavior of the block copolymers using UV/visible spectrophotometer.