en Health Services, Quality of Life and Outcomes Original/Research Article <strong>Introduction</strong>: Iron oxide nanoparticles, owing to their very small size and superparamagnetic properties, have been considered a potential candidate for several medical&nbsp;applications such as magnetic cell separation, magnetic resonance imaging (MRI),&nbsp;magnetic targeted drug delivery magnetichyperthermia. The present study aimed to&nbsp;synthesize and evaluate the characteristics of superparamagnetic iron oxide nanoparticles (SPIONs) and determine the mechanism by which they induce cell death in the&nbsp;presence of an extremely low-frequency magnetic field (ELMF).<br> <strong>Methods:</strong> First, SPIONs were synthesized using the chemical co-precipitation method and then characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. A vibrating-sample&nbsp;magnetometer (VSM) was used to measure the magnetic properties of the nanoparticles. Human MCF-7 breast cancer cells were treated with different concentrations of&nbsp;SPION in the absence and presence of a 50-Hz ELMF for 24 and 48 h. Cytotoxicity&nbsp;and cell viability percentage in the treated cells were measured by the MTT (3-(4,5-di-<br> methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.<br> <strong>Results:</strong> DLS and TEM analyses indicated that the SPIONs have an average size of&nbsp;less than 30 nm and they are superparamagnetic. VSM analyses also confirmed the&nbsp;superparamagnetic nature of the nanoparticles. The MTT assay indicated that high&nbsp;concentrations of SPIONs induced death in MCF-7 cells. In the groups treated with&nbsp;ELMF+SPIONs, cell death increased sharply compared with that in the groups treated&nbsp;with each treatment alone (P&le;0.05).&nbsp;<br> <strong>Conclusions: </strong>It seems that a 50-Hz ELMF in the presence of SPIONs led to cell death&nbsp;due to local heating. Superparamagnetic Iron Oxide, Extremely Low-Frequency Magnetic Fields (ELMFs), X-ray Diffraction 13 21 http://mcijournal.com/browse.php?a_code=A-10-136-1&slc_lang=en&sid=1 Mohammad Satari 10031947532846001509 10031947532846001509 Yes Department of Biophysics, Faculty of Biological Science, Tarbiat Modares University, Tehran, Iran Nazanin Haghighat 10031947532846001510 10031947532846001510 No Department of Biophysics, Faculty of Biological Science, Tarbiat Modares University, Tehran, Iran Fatemeh Javani Jouni 10031947532846001511 10031947532846001511 No Department of Biophysics, Faculty of Biological Science, Tarbiat Modares University, Tehran, Iran Parviz Abodolmaleki parviz@modares.ac.ir 10031947532846001512 10031947532846001512 No Department of Biophysics, Faculty of Biological Science, Tarbiat Modares University, Tehran, Iran