SAPO-11 and SAPO-31, two medium pore molecular sieves, were synthesized from aqueous and non-aqueous (ethylene glycol) media. Their acidities (by TPD of pyridine) and their catalytic activities in the isomerization of n-hexane are compared. Samples synthesized from non-aqueous medium possess more acidity and higher activities than those obtained from aqueous medium. Si-29 MAS NMR studies suggest greater substitution of P5+ by Si4+ and lower concentration of silica islands in the samples synthesized from non-aqueous medium Both SAPO-11 and -31 produce predominantly the monomethyl isomers due to their medium size pores. The activity studies were carried out over Pt-loaded samples in the presence of H-2.