Silicon oxycarbide (SiOC) ultrafine fibers with uniform distribution were prepared via electrospinning of polycarbosilane (PCS)/polystyrene followed by oxidation and pyrolysis at 1100 degrees C. The diameter of SiOC fibers ranged from 500 to 900 nm through adjusting PCS concentration. The average tensile strength of SiOC fiber mat was 8.88 MPa. The obtained SiOC fibers also displayed outstanding thermal stability and chemical resistance, making them promising materials as smart filters and catalyst supports in harsh environment.