Solid acid catalysts are promising for the conversion of cellulosic materials into soluble sugars and have the characteristics that they are environment-friendly and recoverable. However, the existing catalytic systems showed low efficiency, leading to high-energy consumption and generation of by-products. Nano-catalysts can be used to improve many aspects of solid acid catalysts. Nano-catalysts are defined as solid catalysts with particle size in the nanometer level (usually ~100nm), and mainly used in acid-catalyzed organic reactions, such as hydrogenation, oxidation, alkylation, transesterification, condensation, and polymerization. Nano-catalysts can be used for most of the reactions catalyzed by traditional solid acid catalysts. Com­pared with traditional solid acid catalysts, nano-catalysts usually showed improved structural and textural properties in terms of high active site loading, small crystalline size, high surface area and pore volume, and high catalytic activity and selectivity. Moreover, most traditional solid acid catalysts can be used for synthesizing nano­catalysts by supporting acidic sites on nano-carriers or directly preparing nano-scale particles. Up to now, nano oxides are mostly studied supports.