A solid acid catalyst was prepared from masson pine alkali lignin in waste liquor of soda pulping by a combined process of chemical activation, carbonization, and sulfonation. The lignin-derived solid acid (LDSA) was characterized by FESEM, XRD, FTIR, TGA, XPS, BET analyses, and acid-base back titration. The carbonaceous material had high thermal stability and large specific surface area (488.4 m²/g), and the structural analyses showed that it was composed of amorphous carbon bearing -SO₃H, -COOH, and phenolic -OH groups. The lignin-derived catalyst was then applied to the hydrolysis of a microcrystalline cellulose (MCC) in aqueous system, and the yield of total reducing sugars was found to be 46.1%. It was proposed that good adsorption capacities of cellulose and desorption property of glucose on LDSA probably contributed to efficient catalytic hydrolysis.