A mesoporous siliceous material of MCM-41 type was characterized by nitrogen adsorption, X-ray diffraction, and Fourier transform infrared spectroscopy. Its pore diameter, external and internal surface, pore volume, wall thickness, and pore wall density were determined. Special attention was paid to sample aging and its stability toward temperature, water vapor, and mechanical compression, aiming at using this material in industrial applications such as adsorption or catalysis. Calcined MCM-41 loses an important part of its mesoporosity during aging under ambient temperature, pressure, and humidity conditions but then becomes stable after 3 months, still retaining a noticeable porosity. The aged MCM-41 can withstand temperatures up to 873 K and uniaxial compressions up to 100 MPa without too much damage. After contact with water vapor at 358 K, the porous structure was totally destroyed and an amorphous phase was obtained.