To further improve and upgrade the existing functions of carbon fibers, and to endow the carbon fiber with new and desired functions, the most effective and economic way is to create nanostructures on the carbon fiber surface. The carbon fibers with nanostructures grown on the surface, or namely nanostructured carbon fibers, not only maintain the intrinsic high strength, light weight, high thermal conductivity of carbon fiber, but also obtain significant functional enhancements in mechanical properties, interfacial bonding and electrocatalytic property. Different kinds of nanostructures, such as nanoparticles, nanorods, nanotubes, nanosheets, and nanoflowers, are controllably grown on the surface of carbon fibers by using various kinds of techniques, including chemical vapor deposition (CVD), laser ablation, microwave treatment, and hydrothermal process. These multiscale, multifunctional nanostructured carbon fibers not only add new and interesting branches to the carbon fiber family, but also pave the way for the application of carbon fibers in next-generation fiber-reinforced composite, energy storage device and green energy production.