Hydrothermal conversion of lignin was conducted in subcritical temperatures of 300-370 degrees C and residence times of 0.5-10 s at a pressure of 25 MPa. This additional work (subcritical conditions, 300-370 degrees C) was used as a comparison with our previous study (supercritical conditions, 390-450 degrees C) to further investigate the temperature effect on lignin decomposition. Subsequently it was our aim to examine its overall reaction kinetics at wider temperature range, and conclusively we determined each of the reaction natures (radical or ionic reaction) as deduced previously in our original proposed lignin conversion pathways. Due to the change in the properties of water under sub- and supercritical conditions, ionic reactions were expected to deviate from Arrhenius behavior. This was caused by the affected stability of the ions in the reaction from the change in the dielectric constant and ionic product. However, radical reactions could not be expected to be affected by the change in the dielectric constant or ionic product, thus Arrhenius behavior could be expected. Lignin conversion under subcritical conditions occurred rapidly although a higher degree of depolymerization was achieved under supercritical temperatures. In addition, supercritical conditions tremendously enhanced char formation compared to subcritical conditions. This was conclusive evidence that radical reaction played a vital role in char formation mechanism. In addition, the rate constant of the overall lignin decomposition under both sub- and supercritical conditions was observed to obey Arrhenius behavior; however, some of the reactions in the proposed network deviated from this behavior in the supercritical region.