Targeted drug delivery is a promising approach to overcome the limitations of classical chemotherapy. In this respect, Imatinib-loaded PEG-modified magnetic nanoparticles were prepared as a pH sensitive system for targeted delivery of drug to tumor sites by applying a magnetic field. The proposed magnetic nanoparticles were prepared through modification of magnetic Fe3O4 nanoparticles with PEG400 and then Imatinib. The structural, morphological and physicochemical properties of the synthesized nanoparticles were determined by different analytical techniques including energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and X-ray diffraction (XRD). UV/visible spectrophotometry was used to measure the Imatinib contents. Drug loading and release profile of the prepared particles was investigated. The results demonstrated that Fe3O4@PEG acts as a pH responsive nanocarrier in releasing the loaded Imatinib molecules. Furthermore, the Fe3O4@PEG/Imatinib nanoparticles displayed cytotoxic effect against MCF-7 breast cancer cells.