A drug delivery system based on dual responsive units was developed. An appealing pH- and thermo-responsive triblock terpolymer as the drug carrier was synthesized by RAFT polymerization of N-isopropyl acrylamide and methacrylic acid monomers using PEG-RAFT agent. The FeO magnetic nanoparticles were synthesized by co-precipitation of Fe salts. Synthesized samples were characterized by FT-IR, XRD, GPC, SEM and TEM. The dual responsive behaviour and self-assembly of the triblock terpolymers in aqueous solution were investigated using UV-vis transmittance and DLS. Based on the results of DLS and TEM, the average size of micelles was 170, 125 and 30 nm. The triblock terpolymer was used as a chemotherapy drug carrier and doxorubicin as a model drug. The release rate of the drug at two different temperatures (37 °C and 42 °C) and pHs (5.8 and 7.4) was studied. The in vitro cytotoxicity assay of free doxorubicin and drug-loaded magnetic nanoparticles was studied. The MTT assay exhibited that these polymers are biocompatible and no toxicity. As well, IC of the DOX-loaded triblock terpolymer in MTT test demonstrated that these systems could be suitable for the treatment of cancer.