We investigated about yellowing phenomenon of the light protect film-coated tablet which contains quinolone antibacterial agent using THz and Raman spectroscopy. Anatase-type titanium dioxide (IV) (anaTiO 2 ) is usually used for light-shielding film coating, but it has photocatalytic property. UV exposed Ciprofloxacin hydrochloride monohydrate (CPFX.HCl.H 2 O), and mixture of anaTiO 2 and CPFX.HCl.H 2 O, etc. were measured using THz and Raman spectroscopy. According to spectral analysis, it is indicated that a photocatalytic effect of anaTiO 2 would promote dehydration and amorphillization of CPFX.HCl.H 2 O. It suggests that spectroscopic analysis of THz region is applicable to detect degradation of CPFX.HCl.H2O due to photocatalytic reaction of anaTiO 2 .