Magnetic Fe3O4-polyhedral oligomeric silsesquioxanes (POSS) particles with Si-OH were prepared by hydrosilylation reaction between the Fe3O4-SiH and POSS with hydroxyl and vinyl groups. The magnetic Fe3O4-POSS particles were characterized by using transmission electron microscopy, scanning electron microscopy, Fourier transform infrared absorption spectroscopy, thermogravimetry, and vibrating sample magnetometry. The magnetic saturation value of Fe3O4-POSS particles was 18.77 emu/g. Polyacrylonitrile (PAN)/Fe3O4-POSS nanofibers mats were subsequently fabricated by electrospinning technique. The electret properties of PAN/Fe3O4-POSS nanofibers mats and their aerosol filtration property as electrets filter media were characterized. The stability of the surface potential was remarkably improved and the surface potential retention reached 50% for PAN/Fe3O4-POSS mats with 1 wt% Fe3O4-POSS. Compared with pure PAN, the charge retention of PAN/Fe3O4-POSS was increased by 21% and reached 52.40%. Moreover, the collection efficiency increased and the filter resistance decreased when the PAN nanofibers with Fe3O4-POSS were used as electrets filter media. Our study provided an effective method to prepare novel filter materials with high efficiency and low resistance.