The preparation of hyperfunctional carbon black by grafting of hyperbranched polyester onto the surface was investigated. The grafting of hyperbranched polyester onto carbon black surface was achieved by two methods according to hyperbranched polyester synthesis methodology: (1) step-wise propagation of the hyperbranched polyester from surface carboxyl and phenolic hydroxyl groups on the surface through the self-polycondansation of 2,2'-bis(hydroxymethyl)propionic acid (bis-MPA) in the presence of p-toluenesulfonic acid (p-TSA) as a catalyst and (2) one-pot grafting of hyperbranched polyester onto carbon black through the self-polycondensation of bis-MPA in the presence of p-TSA. It was found that hyperbranched polyester was successfully grafted onto carbon black surface by both step-wise and one-pot methods: the percentage of grafting reached 160% in both reaction systems. The hyperbranched polyester-grafted carbon black gave a stable colloidal dispersion in tetrahydrofuran. The results indicate that the grafting of hyperbranched polyester onto carbon black surface is very effective on the modification of dispersibility of carbon black in solvents. The grafting technique would provide a facile route to prepare hyperfunctional carbon black having terminal hydroxyl groups. (C) 2007 Elsevier B.V. All rights reserved.