Mixed oxides derived from hydrotalcites by thermal decomposition are promising catalysts for transesterification reactions. To gain insight into its action mechanism, methanol O-H bond activation was analyzed over Mg-Al mixed oxides using in-situ DRIFT spectroscopy to follow adsorbed species. After methanol adsorption, non-dissociative and dissociative species were identified. Dissociative adsorption resulted in two types of methoxy groups, type I or monodentate methoxy species and type II or bridging methoxy species. Catalytic tests of methanolysis of triacetin have shown a trend where, the higher the amount of adsorbed monodentate methoxy species the higher the catalytic activity of transesterification reaction.