Zn0.5Fe2.5O4 nanoparticles (NPs) of 22nm are synthesized by one-pot approach and coated with silica for magnetic hyperthermia agents. The nanoparticles exhibit superaramagnetic characteristics, high specific absorption rate (SAR) (1083 wg-1, f=430 kHz, H=27 kAm-1), large saturation magnetization (Ms=85emug-1), excellent colloidal stability and low cytotoxicity. The cell uptake properties have been investigated by Prussian blue staining, transmission electron microscope (TEM) and inductively coupled plasma mass spectrometer (ICP-MS), which resulted in time dependent as well as concentration dependent internalization. The internalization appeared between 0.5h to 2h, the NPs were mainly located in the lysosomes and kept good dispersion after incubation with human osteosarcoma MG-63 cells. Then, the relationship between cell uptake and magnetic hyperthermia performance was studied. Our results showed that the hyperthermia efficiency rest with the amount of internalized NPs, which was depended on the concentration and incubation time. Interestingly, the NPs could still induce tumor cells to apoptosis/necrosis when extracellular NPs were rinsed, but the cell kill efficiency is lower than no rinse groups, which indicate that local temperature rise rather than mechanical mechanism is the main factor that induce tumor cells death. Our findings suggest that this high SAR and biocompatible silica coating Zn0.5Fe2.5O4 nanoparticles could serve as a new agents for magnetic hyperthermia.