TPA(tungstophosphoric acid), a typical heteropoly acid, was impregnated on SBA-15 to modify the acidic property of the mesoporous catalyst. The TPA was highly dispersed on the SBA-15 which has large surface area confirming by nitrogen adsorption, X-ray diffraction, and infrared spectroscopy. According to the result of in-situ FTIR spectroscopy using pyridine as a probe molecule, it was revealed that silanol group was gradually decreased with increasing the loading amount of TPA, and that new acidic site different from that of pure TPA was generated resulting in the enhancement of catalytic activity. TPA could act as a promoter when loaded on SBA-15 by relatively small amount, but the catalytic activity was greatly decreased due to the loss of silanol group as an active site when a large amount of TPA was loaded.