It was found that the cationic ring-opening polymerization of δ-valerolactone (VL), e-caprolactone (CL), and β-propiolactone (PL) was initiated by carbon black containing CO+ClO groups, which were introduced by the reaction of COCl groups with AgClO4. The polyester was propagated from CO+ClO groups and effectively grafted onto carbon black surface. The polymerizability of these lactones by CO+ClO groups decreased in the following order: VL > CL > PL. The increasing temperature of the polymerization caused an increase in the rate of the chain transfer reaction of the growing chains and brought about the decrease of grafting ratio of polyester onto carbon black.