A series of sulfo-group-bearing mesoporous silica (SBA-15) catalysts were prepared using a one-step hydrothermal synthesis method. The effect of preparation conditions on the structure and acidic nature of the prepared solid acid catalysts was investigated. The characterization results of the prepared solid acid catalysts indicate that most of the sulfur atoms in mercaptan were oxidized and converted into sulfo groups through a reaction with hydrogen peroxide and that the SBA-15 structure was retained in all the catalysts after the oxidation. The catalytic performance of the prepared solid acid catalysts in the saccharification of cellulose and rice straw was investigated; an autoclave was used for the saccharification. A maximum glucose yield of 27% and a maximum total monosaccharide yield of 21% were obtained when the saccharification of cellulose and rice straw was carried out using a MPS-D catalyst, respectively.