The structural features, chemical properties, and methods of inactivation of the amorphous Ti species in TS-1 are investigated. The formation of the amorphous Ti species, which is composed of fragments of Ti–O–Ti chains, is confirmed by the Raman band at 700cm−1. The presence of the amorphous Ti species severely decreases the catalytic performance of TS-1 by causing byproduct formation and H2O2 decomposition. The sulfosalt impregnation method can easily reduce the adverse effects of the amorphous Ti species. Display omitted ► New Raman feature at 700cm−1 was assigned to the amorphous Ti species in TS-1. ► The amorphous Ti species compose by hexacoordinated Ti–O–Ti linkages. ► The amorphous Ti species enhancing the acidity and causing the H2O2 decomposition. ► The sulfosalt impregnation can reduce the adverse effect of the amorphous Ti species. 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 700cm−1, which is closely related to the UVDRS band at 260–280nm, 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.