Large-scale practical applications of fullerene (C₆₀) in nanodevices could be significantly facilitated ifthe commercially available micrometer-scale raw C₆₀ powder were further processed into a one-dimensional nanowire-related polymer displaying covalent bonding as molecular interlinks and resembling traditional important conjugated polymers. However there has been little study thus far in this area despite the abundant literature on fullerene. Here we report the preparation and characterization of such a C₆₀-based polymer nanowire, (-C₆₀TMB-)_n, where TMB=1,2,4-trimethylbenzene, which displays a well-defined crystalline nanostructure, exceptionally large length-to-width ratio and excellent thermal stability. The material is prepared by first growing the corresponding nanowire through a solution phase of C₆₀ followed by a topochemical polymerization reaction in the solid state. Gas chromatography, mass spectrometry and ¹³C nuclear magnetic resonance evidence is provided for the nature of the covalent bonding mode adopted by the polymeric chains. Theoretical analysis based on detailed calculations of the reaction energetics and structural analysis provides an in-depth understanding of the polymerization pathway. The nanopolymer promises important applications in biological fields and in the development of optical, electrical, and magnetic nanodevices.