Abstract: Single-walled carbon nanotubes (SWCNTs) were functionalized by the covalent attachment of 2-propanol-2-yl radicals to their surface. These radicals were generated by photolysis of 2-hydroxy-2-methyl-1-phenyl-1-propanone under ultraviolet (UV) light. Pristine SWCNTs were dispersed in a tetrahydrofuran solution, and then free radicals were attached to their surface when the solution was subjected to UV irradiation. The functionalization of SWCNTs was evidenced by UV/visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermal gravimetric analysis-mass spectrometry (TGA-MS) and high resolution transmission electron microscopy (HRTEM). UV/visible results indicated a loss of Van Hove singularities because of the covalent functionalization. The modification was further proved by FTIR. Raman spectra showed that the intensity ratio of the G band and D band (IG/ID) decreased for the functionalized SWCNTs. TGA-MS also showed a signal corresponding to m/z 59 at 400℃, indicating the presence of 2-propanol-2-yl groups. HRTEM and solubility data proved that the sidewall functionalization dissociated the bundle structure, improved the solubility in common organic solvents and retained the original electronic structure of the SWCNTs without severe modification that damages the nanotubes.