This　paper　investigates　synthesis　and　characterization　of　smart　polymer　brush-modified　magnetic　nanoparticles　(SPB-MNPs).　Magnetic　nanoparticles　(MNPs)　modified　with　poly(poly(ethylene　glycol)　monomethacrylate　(poly(PEGMA))　brush　were　first　functioned　with　activated　pyridyldithio.　Then,　MNPs　functioned　with　pyridyldithio　(MNPs-PEG-PDT)　were　conjugated　with　4-diamino-6-mercaptopyrimidine　(DMP)　to　form　SPB-MNPs　via　stimuli-responsive　disulfide　linkage.　Fourier　transform　infrared　spectra　(FTIR)　was　used　to　monitor　the　preparation　process　of　MNPs-PEG-PDT.　MNPs-PEG-PDT　is　very　highly　reactive　toward　DMP.　The　disulfide　linkage　of　SPB-MNPs　can　be　cleaved　by　reduced　glutathione　(GHS).　The　concentration　of　GHS　plays　an　important　role　in　controlling　the　cleaved　efficiency.　The　optimum　concentration　of　GHS　to　release　DMP　is　in　the　millimolar　range.