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Ceramic nanofibers with robust mechanical properties, high-temperature resistance, and superior thermal insulation performance are promising thermal insulators used under extreme conditions. However, developing of ceramic fibers with both low solid thermal conductivity (λ s ) and low infrared radiation thermal conductivity (λ r ) is still a great challenge. Herein, according to the Ioffe-Regel limit theory, we report a novel SiZrNOC nanofiber membrane (NFM) with a typically amorphous structure by combining the electrospinning method and high-temperature pyrolysis technique in a NH 3 atmosphere. The prepared SiZrNOC NFM has a high tensile strength (1.98±0.09 MPa), excellent thermal stability (1100 ℃ in air), and superior thermal insulation performance. The thermal conductivity of SiZrNOC NFM was 0.112 W•m −1 •K −1 at 1000 ℃, which is obviously lower than that of the traditional ceramic fiber membranes (> 0.2 W•m −1 •K −1 at 1000 ℃). In addition, the prepared SiZrNOC NFM-reinforced SiO 2 aerogel composites (SiZrNOC f /SiO 2 ACs) exhibited ultralow thermal conductivity of 0.044 W•m −1 •K −1 at 1000 ℃, which was the lowest value for SiO 2 -based aerogel composites ever reported. Such superior thermal insulation performance of SiZrNOC NFMs was mainly due to significant decreasing of solid heat conduction and thermal radiation by the fancy amorphous microstructure and high infrared shielding compositions. This work not only provides a promising high-temperature thermal insulator, but also offers a novel route to develop other high-performance thermal insulating materials.