Abstract: A series of mesocarbon microbeads (MCMB) and small carbonaceous particles (SCP) with size less than 0.5μm were prepared from a coal tar pitch containing quinoline insolubles at 410℃ by varying the holding time. By analyzing softening point and solubility of the as-received mesophase pitches, morphologies of the MCMB and SCP, and cross-section area of the MCMB, it was found that the development of the MCMB formed through heterogeneous nucleation did not follow the coalescence development as the homogeneous nucleation of MCMB but kept to the process of Building from Spherical Basic Units (BSBU), in which spherical SCP were the basic units to build MCMB spheres. During this process, the viscosity of the system was the important factor that had great influence in the production of MCMB and SCP. The internal microtextures of MCMB were none of the three model structures of global type, onion type and concentric circles type, but a complex structure with the carbon layers converging at one or two points. With increased the holding time, the structures of MCMB did not inherit the previously formed structures, but the carbon layers changed and rearranged into new types. The main tendency of the carbon layer rearrangement in MCMB was not to make the carbon layers parallel but to make them become larger.