The effects of primary quinoline insoluble (PQI) on the formation process of mesocarbon microbeads (MCMBs) have been investigated through comparison of microstructural characteristics of PQI and MCMBs, which were comprehensively identified by Fourier transform infrared, solid-state C-13 nuclear magnetic resonance and X-ray diffraction. The results showed that PQI had similar polyaromatic structure to MCMBs in terms of carbon aromaticity, which indicated that PQI could overcome the high energy barrier of a new mesophase formation and decrease the activation energy of MCMBs formation. Thus, it was concluded that PQI could act as the nuclei for mesophase growth. The nucleation of PQI was further justified by the of-course growth of the secondary MCMBs. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.