Carbonaceous mesophase is an excellent precursor for preparing high performance carbon materials. The structure of carbonaceous mesophase could be affected by the raw material and the condensation conditions. In the present work, the influence of inorganic impurities in coal tar pitch on the structures of the mesophase formed was investigated by adding some inorganic materials, such as nano-scale silicon dioxide and micron-scale alumina. Scanning electronic microscopy (SEM) was used to observe the morphology and cross-sectional texture of the mesophase spheres. It was found that inorganic impurities would influence the structure of the mesophase and the size of inorganic materials was a key factor for affecting the final structure of the mesophase. The microtexture of the MCMB formed in the coal tar pitch without inorganic impurities tends to be global type. Nano-scale silicon dioxide changed the forming mode of MCMB from homogeneous nucleation to heterogeneous nucleation and the MCMB formed was built up with small spheres with the size of less than 3.5μm. Micron-scale alumina particles could not change the mode of nucleation of MCMB but were enwrapped in the MCMB and distorted the microtexture layers of MCMB.