Core–shell Fe₃O₄–SiO₂magnetic nanoparticles (MNPs) have been synthesized using a simple synthesis procedure at different temperatures. These MNPs are used to investigate the effect of surface coatingon specific absorption rate (SAR) under alternating magnetic field. The temperature achieved by silicacoated Fe₃O₄is higher than that by uncoated MNPs (Fe₃O₄). This can be attributed to extent of increase inBrownian motion for silica coated MNPs. The sample prepared at optimized temperature of 80°C shows the highest SAR value of 111 W/g. It is found that SAR value decreases with increase in shell thickness.The chemical stability of these samples is analyzed by leaching experiments at pH 2–7. The silica coatedsamples are stable up to 7 days even at pH 2. Biocompatibility of the MNPs is evaluated in vitro by assessingtheir cytotoxicity on L929 and human cervical cancer cells (HeLa cells) using sulforhodamine-B assay.Their hyperthermic killing ability is also evaluated in HeLa cells using the same method. Cells treated withMNPs along with induction heating show decrease in viability as compared to that without inductionheating. Further, cell death is found to be ~55% more in cells treated with silica coated MNPs underinduction heating as compared to untreated control. These results establish the efficacy of Fe₃O₄–SiO₂ prepared at 80°C in killing of tumor cells by cellular hyperthermia.