Ultrafine SiO 2 glass fibers have been produced by direct oxidation and combustion of Si particles in air flow. Two kinds of fibers are observed, including submicron nodulated fibers and rod-like nanofibers. EDS analysis reveals that the chemical composition of the fibers agrees well with SiO 2 and the total content of impurities is below 2.0%. It is proposed that the formation of the fibers is related to air flow and includes three steps, viz. spherical process and attachment of Si particles, oxidization, and smoothing of SiO 2 chains. Due to the short reaction period and fast cooling rate, the SiO 2 fibers have no time to crystallize and remain as glass.