Modification of an isotropic precursor pitch (IMP) for general performance carbon fibre (GPCF) was carried out by blending isotropic and mesophase pitches (IP and MP, respectively), both of which were synthesized from naphthalene using HF/BF3 as catalysts because they carried a large amount of naphthenic hydrogens. Both IP and MP were miscible with IMP at temperatures higher than their softening points. The softening point of the blended pitch dropped remarkably, being lower than 200-degrees-C with 40% 1P. Such lower softening points made spinning much smoother. Modification also enhanced the stabilization reactivities of pitch fibre, the time required for the sufficient stabilization at 270-degrees-C decreasing by 20 and 30 min by blending with 20% IP and 20% MP, respectively. The mechanical properties of the resultant carbon fibres were also improved.