A study of hydrothermal stability, performed in boiling water under static conditions, of MCM-41 materials containing different titanium content, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium ethoxide and octadecyltrimethyl- ammonium bromide is presented. The behaviour is compared with pure silica grades prepared by a similar procedure. The samples were characterised by X-ray diffraction, adsorption of nitrogen at 77K and diffuse reflectance UV–Vis spectroscopy. It was found that the stability improves as the amount of titanium increases and that Ti-MCM-41 samples prepared with Si/Ti≤50 are significantly stable. After 12h in boiling water the pore size uniformity was practically maintained and only a small decrease in pore volume (5-9%), total surface area (2-7%) and mesopore width (3%) and a slight increase in pore wall thickness (3-6%) occurred. In contrast, some degradation of the MCM-41 structure for the pure silica and the lower Ti content (Si/Ti=100) samples was observed with the effect being less pronounced for the latter. The higher hydrothermal stability of titanium substituted samples is probably correlated with a higher degree of polymerisation of the pore walls and with the presence of extra framework titanium.