When mesophase pitches were prepared from coal tar pitch by heat treatment with temperatures and superficial velocity of N₂ gas respectively, carbonization characteristics, transforming course and step process characteristics according to mesophase contents were investigated. Types of transforming mesophase were very different on heating temperature and superficial velocity of N₂ gas. At higher temperature, forming rate of mesophase was high, but solubility by solvent and melting temperature decreased and became high, respectively. The mesophase contents increased by superficial velocity of N₂ gas(below 120 cm/sec), but after that, even though superficial velocity of N₂ gas increased, there was no effects on transforming mesophase. The mesophase contents in pitches heat-treated did not agree with QI contents. On the other hand, the amount of β-resin was the highest at 15-40 vol% of mesophase contents and became higher as treating temperatures decreased, considering on blowing rate of N₂ gas, that was the highest at 20 vol%, after that. became constant and higher as blowing rate decreased. It is found that atomic ratio(C/H) was dependent not on superficial velocity of N₂ gas but heat-treating temperatures. Moreover, mesophase pitch behaved as typical non-newtonian fluids and showed viscosity variation for the fluidity according to mesophase contents. So, preparing mesophase of superior property was needed lower temperature and optimum ranges of superficial velocity of N₂ gas on transforming mesophase.