Pyrene-capped polystyrene (PyPS) with various molecular weights ((M) over bar (n)) was synthesized through the anionic polymerization method and characterized using UV, Fourier transform infrared and NMR spectroscopy and gel permeation chromatography. The polymers were then used for non-covalent functionalization of pristine single-walled carbon nanotubes (SWNTs). The functionalization efficiency was assessed by measuring the SWNT dispersibility in chloroform. In the presence of PyPS, the dispersibility can be as high as 372.5 mg L(-1), and the dispersions containing more than 1.25 mg mL(-1) of PyPS are very stable with no solid deposits observed after being centrifuged at 5000 rpm for 15 min. Once the PyPS concentration is converted to the molar concentration of the pyrene unit and the dispersibility redefined as nanotube content per molar pyrene unit, the renewed dispersibility is found to be independent of (M) over bar (n) of PyPS within the detected (M) over bar (n) range. For a certain PyPS polymer, however, both nanotube dispersibility and dispersion stability are strongly dependent on the PyPS concentration. These results suggest that PyPS may be used as an excellent dispersant for subsequent preparation of polystyrene/SWNT composites. (C) 2011 Society of Chemical Industry