To date, concentrated sulfuric acid hydrolysis is the most effective process to recover the maximum yield of monomeric sugars from woody biomass because concentrated sulfuric acid can completely swell and hydrolyze cellulose. During this process, sulfuric acid lignin is quantitatively produced as a by-product, which is difficult to use because of self-condensation between the lignin molecules under acidic conditions. In this study, to achieve a high yield of both sugars and lignin, we aimed to valorize the lignin with a unique additive,t-butyl alcohol, in the concentrated sulfuric acid hydrolysis of softwood. Whent-butyl alcohol was added, sugar yields were unchanged and were nearly equal to the amount of compositional sugars. Thermoplastic lignin with good solubility in acetone was successfully recovered in a yield higher than 40%. The economic efficiency of the concentrated acid hydrolysis was significantly improved by upgrading the lignin. Thus, this unique process could be a new candidate in the realization of sugar platform biorefineries.