Medium-pore SAPO-11 and SAPO-31 molecular sieves were synthesized from aqueous and non-aqueous (ethylene glycol) media. All the samples were characterized by XRD, SEM, N-2 adsorption (BET analysis), TGA-DTA, pyridine-TPD, Al-27 MAS-NMR, and Si-29 MAS-NMR. The samples synthesized from non-aqueous medium possess higher acidity due to higher substitution of Si4+ at P5+ sites and less silica island formation, as evidenced from 29Si MAS-NMR spectra. It is possible to incorporate more silicon in the samples by synthesis in ethylene glycol medium. The SAPOs synthesized from non-aqueous medium show higher activity for the isomerization of m-xylene. (C) 2004 Elsevier B.V. All rights reserved.