Polybenzimidazole (PBI) is shown to individually dissolve/disperse single-walled carbon nanotubes (SWNTs) in N,N-dimethylacetamide (DMAc), which is demonstrated by vis-near IR absorption and photoluminescence spectroscopy and atomic force microscopy observations. By casting these dispersions, SWNTs/PBI composite films were successfully fabricated on substrates without any sign of macroscopic aggregation. The thermal stability and mechanical properties of the composite films were investigated using thermogravimetric analysis (TGA) and tensile tests, respectively, and it was found that, first, the addition of SWNTs to PBI does not deteriorate the thermal stability of the matrix film, and second, the mechanical properties of the PBI film were reinforced by ca. 50% with only 0.06 wt % addition of the SWNTs to the film without reducing the thermal stability of the PBI. Raman spectroscopy of the composite films revealed the existence of an interaction between the PBI and the SWNTs. The individual dissolution of the SWNTs and efficient reinforcement of the PBI are due to the π–π interaction between the PBI and the sidewalls of the SWNTs.