The kinetics of mesophase transformation of two coal tar pitches (CTP) with different primary quinoline-insoluble (QI) content had been studied.It was clarified that the mesophase transformation of CTP studied was an autocatalytic type reaction. The rate law and rate constants for the mesophase transformation at holding temperature of 390 degrees C, 410 degrees C and 450 degrees C were determined and the rate constants of mesophase transformation follow the Arrhenius equation. Primary QI of CTP decreases the activation energy from 210.1 kJ/mol to 175.8 kJ/mol, and the pre-exponential factor from 2.12 X 10(13) l/h to 6.29 X 10(10) l/h; its influence on the rate constants is irregular.