β-Resin was extracted by solvent separation of refined coal tar pitch. Several analytical methods revealed that β-resin had a better aromatic plane packing structure and a higher number of carbon residues, making it ideal for mesophase transformation. The mesophase transformation process of β-resin (the formation of liquid-crystalline spheres, the growth of mesophase spheres, and the coalescence and disintegration of mesophase spheres) was observed in situ using a polarizing microscope with a hot stage. Moreover, the mesophase transformation mechanism of β-resin was investigated at each transformation stage. The mesophase content and mesophase transformation kinetics were analyzed based on the area method and quinoline insoluble (QI) substitution method. Both methods revealed changes in the mesophase content of β-resin. However, the test results of the two methods were slightly different at the initial stage of mesophase transformation and tended to be consistent during the later stage.