Mesoporous titanosilicates (MTS-9A) with thermally stable titanium species were synthesized by adding ammonium salts in the preparation procedure. Characterization results show that hexagonal mesoporous titanosilicates (MTS-9A) contain primary and secondary structural building units of zeolite in the framework, in a similar manner to MTS-9. The promoted condensation of Ti-containing silica network in MTS-9A leads to higher thermal stability of four-coordinated titanium species compared with MTS-9, as evidenced by UV-vis and Si-29 NMR spectra. Catalytic tests indicate that MTS-9A samples show high activity in hydroxylation of both small (phenol) and bulky reactants (2,3,6-trimethylphenol) before and after calcination. Moreover, the recycled catalyst retains high conversion, confirming the high thermal stability of titanium species. (c) 2006 Elsevier Inc. All rights reserved.