In this work MAPO-11 molecular sieve was prepared with several degrees of magnesium substitution. The syntheses were carried by using phosphoric acid, pseudo-boehmite and magnesium acetate as sources of structural elements and diisopropylamine as the structure-directing agent. The samples were characterized by powder X-ray diffraction, thermogravimetry, infrared spectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy and elemental analysis. The X-ray diffractograms indicate that the AEL structure is obtained free of contaminating phases up to a magnesium molar ratio of 0.3 in the reaction mixture. Higher levels of magnesium cause the formation of other phases. Thermogravimetry, MAS nuclear magnetic resonance of 3 1 P and infrared spectroscopy confirm the magnesium isomorphous substitution for aluminum up to this magnesium content in the reaction mixture.