The depolymerization of hydrochloric acid sweetgum lignin by hydrotreating in hydrogen-donor solvents in the temperature range of 375–425°C (707–797°F) has been studied. Analysis of the phenolic products showed that the principal depolymerization reactions were the cleavage of ether and Cα–Cβbonds. A maximum yield of approximately 11% monomeric phenols was obtained, with the intermediate compounds for the most part being further degraded into gases and neutral products. The reaction kinetics were found to be first order, with an activation energy of 24 Kcal (100 kJ). The addition of a heterogeneous catalyst did not increase the yield of monomeric phenols.