Novel, freestanding membranes composed of SiO2@Bi2O3 hierarchical core/shell fibers were prepared by a combination of two fabrication methods: electrospinning and hydrothermal reaction. The SiO2@Bi2O3 composite membranes were primarily supported by flexible SiO2 fibers after calcination treatment of electrospun PVA/SiO2 hybrid fibrous membranes. SiO2@Bi2O3 composite fibers were fabricated via a process that entails hydrothermal growth of bismuth precursor nanocoating (Bi-PN) on the surface of SiO2 fibers followed by the thermal treatment of the harvested SiO2@Bi-PN fibers. It was observed that Bi2O3 nanoparticles were well anchored on the surface of SiO2 fibers and the phase transition of Bi2O3 nanoparticles occurred during the thermal treatment of SiO2@Bi-PN composite fibers at different temperatures. The infrared emission rates of the resultant SiO2@Bi2O3 composite membranes were evaluated in comparison with pure SiO2 fibers in 2 ~ 22 μm wavebands. It is theorized that the coating of Bi2O3 nanoparticles contributes to the decrease of infrared emissivity, and the infrared emission properties of SiO2@Bi2O3 composite fibers are related to the phase structures of Bi2O3. The results favourably indicated prospects of SiO2@Bi2O3 composite fibrous membranes for applications in infrared stealth camouflage.