Carbonaceous solid acid (CSA) catalysts with -SO3H, -COOH, and phenolic OH functional groups were prepared by hydrothermal carbonization and sulfuric acid impregnation methods. A maximum furfural (FF) yield of 19.66% from corncob degradation remained stable at 10 runs at 180 degrees C for 170 min while the concentration of sulfuric acid was employed from 2.0 to 0.5 mol/L. The sulfur in CSA catalyst exists in two forms, namely SO42- and -SO3H. The free sulfuric acid and carbon together with -SO3H created good physical contact between the lignocellulose substrate and the solid catalyst in the reaction, and drastically improved the depolymerization rate of hemicelluloses and cellulose to soluble polysaccharide.