Nanometer composite S2O82-/SnO2-TiO2, a novel solid superacid, was prepared by the sol-gel method and its structure was characterized by XRD, TEM, FT-IR and nitrogen adsorption. Results indicated that the composite S2O82-/SnO2-TiO2 had a narrow particle size distribution with an average particle diameter about 15~20nm. S2O82- combined with SnO2-TiO2 resulted in formation of strong acid sites on the surfaces. The surface area of catalysts obviously increased after incorporating SnO2. Nanometer S2O82-/ SnO2-TiO2 composite was used as a catalyst for a-pinene isomerization and the influence of catalyst preparation conditions on its performances were investigated. The optimum condition for superacid catalyst preparation was found to be with 2:1 Sn/Ti mole ratio, S2O82- 1 mol · L-1 of impregnation consideration and toasting temperature of 773K. With 3% of S2O82-/SnO2- TiO2 catalyst dosage at a reaction temperature at 403K for 2 h, the conversion of a-pinene was 98 % and the selectivity to camphene was 62 %.