Abstract: This invention relates to fibrous nanocarbons, especially to ladder-structured and pair-structured fibrous nanocarbons, and the preparation thereof. Specifically, the fibrous nanocarbons of this invention, which are designed to be used for molecular composite materials, fuel cell catalyst supports, organic reaction catalyst supports, gas storage of methane and hydrogen, electrodes or conductors for lithium secondary battery, and electrodes for electric double layered capacitor, are characterized by the graphite-like structure with the sp2 hybrid carbon content of more than 95% per total content; the interlayer spacing (d002, d-spacing of C (002) profiles determined by X-ray diffraction method) of 0.3360 nm˜0.3700 nm; the (002) plane stacking of more than 4 layers (or 1.5 nm); the aspect ratio of more than 10; the fiber cross-section width/thickness of 5 nm˜500 nm; and the ladder-like and pair structure with no continuous hollow core.