Hyperthermia generally means as increasing the temperature of particular region of body to rise 5 °C above the body’s physiological temperature. Here, we investigate the thermal therapy of PEGylated cobalt ferrite nanoparticles prepared by hydrothermal approach on cancerous cell line in the alternative current magnetic field. To characterize of the magnetic nanoparticles (MNPs), scanning electron microscopy, dynamic light scattering, X-ray diffraction, Fourier transform infrared spectroscopy, and vibrating sample magnetometer were used. X-ray diffraction analysis confirmed the spinel phase formation of the MNPs. Cytotoxicity of MNPs using MTT assay on L929 cell lines showed the PEGylated MNPs extraordinary biocompatibility. Specific loss power (SLP) were calculated for neat and PEGylated MNPs in aqueous solution in radio frequency region (300–400 kHz). Power absorbed by neat and PEGylated cobalt ferrite were measured as a function of frequency and MNPs concentration. The maximum SLP was 31.8 W/g for coated nanoparticles (MNPs + PEG) in concentration of 0.0025 gr/mL at applied frequency of 350 kHz. Magnetic fluid hyperthermia of MCF7 breast cancer cells were shown up to 90 percent of cell death in 350 kHz. Simulation studies approved the elevated temperature of the PEGylated MNPs to 42 °C in the tumor after 10 min of MNPs intratumorally injection. This study shows increase in rate of heating in the tumor when the temperature of injected MNPs is approximately equal to the body temperature (i.e. 37 °C).