The aim of this work was to investigate the formation of the inclusion complex between omeprazole (OME), a benzimidazolic derivative and a methylated cyclodextrin, methyl-beta-cyclodextrin (MbetaCD), with an average degree of substitution of 0.5. Inclusion complex between OME and beta-cyclodextrin (betaCD), a natural cyclodextrin, was used as reference. In aqueous media, apparent stability constants (K(s)), which describe the extent of formation of the complexes, have been determined by UV spectroscopy and 1H NMR experiments. The stoichiometry of the complexes was found to be 1:1 mol:mol OME:cyclodextrin (CD) and the value of K(s) was higher for OME:MbetaCD than for OME:betaCD inclusion complexes. Solid binary systems of OME and CDs were prepared by different techniques, namely kneading, spray-drying and freeze-drying. The formation and physicochemical characterization of solid inclusion complexes were investigated by differential scanning calorimetry (DSC), Fourier transform-infrared (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results show that freeze-drying method produces true inclusion complexes between OME and both CDs. In contrast, crystalline drug was detectable in kneaded and spray-drying products. The dissolution of OME from the binary systems was studied to select the most appropriate system for the development of a buccal drug delivery formulation. It was concluded that the preparation technique played an important role in the dissolution behaviour of the drug and the inclusion complex between OME and MbetaCD obtained by spray-drying and freeze-drying allowed better performances.