The present study was focussed on the modelling of the evolution under hear treatment of the so-called gamma, beta and alpha-resins fractions usually used for pitches composition characterization. The model was based on phenomenologic basic mechanisms such as gas-liquid, liquid-liquid mass transfers and chemical reactions with respect to the overall resins assimilated to basic equivalent chemical species. It has been confronted with success to experimental data investigated at three temperature levels (400, 330, 450 degrees C) and eight soaking times (from 0 to 12 h) for two different materials: a petroleum and a coal tar pitch. The identified kinetic parameters were found to be in agreement with usual values encountered in literature for similar basic phenomena. This led to an accurate predictive tool intended to reactor design and optimization as well as pitches reactivity comparison.