Coal-tar pitch is modified with p-methyl benzaldehyde (PMB) in the presence of p-toluene sulfonic acid (PTS). The main characteristics of the modified pitches such as coking value, softening point and solubility are studied in this paper. The molecular structures of the modified pitches are studied using FT-IR and H-1-NMR spectroscopy techniques. In addition, the morphologies of the modified pitches are inspected with SEM, and the optical textures of resultant semi-cokes are characterized by polarized-light microscopy. Results show that the modified pitches have much higher coking value and beta-resins content than the parent pitch. There exist many microfibers with a uniform distribution in the modified pitches. Moreover, the modification results in an improvement in the optical textures of resultant semi-cokes. (C) 2004 Elsevier Ltd. All rights reserved.