Abstract: A small quantity of mesocarbon microbeads (MCMBs) derived from a coal tar pitch were added to another coal tar pitch to investigate the formation and growth mechanism of MCMBs. It was found that new MCMBs were also observed. A further analysis of particle size distributions, morphology and cross-section texture of the new and added MCMBs as well as their total yields showed that the secondary growth of the added MCMBs was mainly driven by physical interactions. The thermal condensation of the pitch included nucleation of raw pitch to form the new MCMBs and secondary growth of the added MCMBs. The two parallel processes competed with each other and the dominating one was determined by the fraction of the added MCMBs. It was concluded that the basic structural units of MCMBs moved from the parent pitch onto the surface of MCMBs during the growth.