The structural properties of mesoporous molecular sieves with MCM-41 type structure were studied by molecular dynamics simulations. The ratio between wall thickness and pore diameter was varied and the stabilization energy of the lattice was determined for a pore diameter range between 15 and 49 Angstrom. With decreasing wall thickness and increasing pore radius an increase of the stabilization energy was observed. Structures with partially interconnected pores and interrupted walls were found to be energetically unstable. Radial distribution functions indicated that the walls of MCM-41 type materials are preferably amorphous.