Cubic mesoporous structures with Ia3d symmetry, such as MCM-48 and large pore Ia3d material (LP-Ia3d), which present different pore size (3.6 and 5.7nm, respectively), have been prepared, characterized and used as drug delivery systems. Ibuprofen and erythromycin have been chosen as drug models for delivery studies. The influence of the pore size at these structures has been studied and the results show that the delivery rate of drugs decreases with the pore size of the matrix. The influence of chemical nature of the pore surface on the delivery process has been also studied. In this case, the hydrophilic pore surface has been modified with hydrocarbon chains (C8 and C18 moieties) and the effect upon drug delivery of hydrophobic drugs like erythromycin has been studied. The results show a noticeable decrease of the delivery rate when the surface of the matrices is modified.