Carbon nanotubes (CNTs) exhibit outstanding mechanical and electrical properties. However, CNT fibers (CNTFs) have still problems in realizing these properties because of the weak forces between nanotubes with many defects of individual CNTs. Here, we report a solid-state coupling reaction with an iodophenyl motif to investigate molecular covalent bridging in CNTFs. The stepwise thermochemical processes were chemical functionalization followed by thermal treatment of CNT surface to induce solid-state coupling reaction for molecular bridge of CNTFs. These molecular-bridged CNTFs presented phenomenal boost in mechanical tensile strength (0.93 N/tex) which is 132% higher than pristine CNTFs without a decrease in electrical conductivity (870 S/cm).