Mesophase spheres were prepared through homogeneous and heterogeneous nucleation from two coal tar pitches with some and nearly without quinoline insolubles. The pitches suffered thermal condensation in a stainless steel reactor at 440 and 410℃ for 1 or 7h, respectively. SEM was introduced as a useful tool to detect the structures of the two kinds of mesophase spheres. As a result of the paper, it was found that the structure of mesophase spheres prepared through homogeneous nucleation was Brooks-Taylor type, which is consistent with the analysis result of optical microscopy. Whereas, the structures of the heterogeneous nucleation mesophase spheres were complex, which were parallel in parts of the structure.