The nature of the amorphous Ti species in titanium silicalite-1 (TS-1) was investigated by UV Raman spectroscopy (UV Raman), UV-vis diffuse reflectance spectroscopy (UVDRS), infrared spectroscopy (IR), and Hammett indicator titration methods. A new Raman feature at 700 cm(-1), which is closely related to the UVDRS band at 260-280 nm, is first assigned to a totally symmetric vibration of hexacoordinated Ti-O-Ti linkages of the amorphous Ti species. The amorphous Ti species in TS-1 can be formed easily under the synthesis conditions in the presence of Na+ or after treatment in ammonia solution. The results reveal that the amorphous Ti species is the main factor in the enhanced acidity and H2O2 decomposition ability of TS-1. A sulfosalt impregnation method has been proved effective in reducing the adverse effect of the amorphous Ti species. (C) 2011 Elsevier Inc. All rights reserved.