ObjectiveTo investigate the bioeffects of extremely low frequency (ELF) magnetic field (MF) (50 Hz, 400μT) and magnetic nanoparticles (MNPs) via cytotoxicity and apoptosis assays on PC12 cells. MethodsMNPs modified by SiO2 (MNP-SiO2) were characterized by transmission electron microscopy (TEM), dynamic light scattering and hysteresis loop measurement.PC12 cells were administrated with MNP-SiO2 with or without MF exposure for 48 h. Cytotoxicity and apoptosis were evaluated with MTT assay and annexin V-FITC/PI staining, respectively. The morphology and uptake of MNP-SiO2 were determined by TEM. MF simulation was performed by Ansoft Maxwell based on the finite element method. ResultsMNP-SiO2 were identified as~20nm (diameter) ferromagnetic particles. MNP-SiO2reduced cell viability in a dose-dependent manner. MF also reduced cell viability with increasing concentrations of MNP-SiO2. MNP-SiO2 alone did not cause apoptosis in PC12 cells; instead, the proportion of apoptotic cells increased significantly under MF exposure and increasing doses of MNP-SiO2. MNP-SiO2 could be ingested andthen cause a slight change in cellmorphology. ConclusionCombined exposure of MF and MNP-SiO2 resulted in remarkable cytotoxicity and increased apoptosis in PC12 cells. The results suggested that MF exposure couldstrengthen the MF of MNPs, which may enhance the bioeffects of ELF MF.