Kraft oak lignin and ricestraw lignin from acetosolve pulping were dissolved in 50/50 mixture of tetralin/m-cresol solvent. The dissolved lignin was reacted in the pressurized autoclave which was operating at $350{sim}500^{circ}C$ of reaction temperature and 10~20 atms of reaction pressure respectively_Hydrogen pressure of 60~80kg/$cm^2$ was exercising into the pressurized autoclave reactor to create thermochemical hydrogenolysis reaction. It was identified by GLC, GC-MS and HPLC that the alkyl-aryl-${eta}$-O-4 ether bond of lignin was cleaved and degraded into various smaller molecules of aromatic compound such as phenols and cresols under the reaction conditions around $300^{circ}C$ and 10 atms of reaction temoerature and pressure. Hydrogenolysis reaction of lignin compound which was done above $500^{circ}C$ of reaction temperature and 20 atms of reaction pressure showed that the amount of aromatic compound such as phenols and cresols degraded from reactant lignin was decreasing with newly present and increasing water out of product mixtures. It was supposed that new aliphatic compound of high molecular weight hydrocarbon is composed due to higher reaction temperature and pressure of hydrogenolysis reaction such as $500^{circ}C$ and 20 atms, even though it was almost impossible, to identify what kind of degraded products it was by HPLC.