A series of SAPO-11 catalyst samples were synthesized by varying source of silica and synthesis time. Products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption and FTIR spectroscopy of pyridine adsorption as well as evaluated towards 1-butene skeletal isomerization. By using waterglass as a source of silica, tridymite phase instead of SAPO-11 was obtained. The combination of colloidal silica and aluminum oxide as sources of silica and alumina resulted in SAPO-11 phase but small amounts of other phases, such as tridymite, were obtained. The number of the acid sites was observed to increase if synthesis time was prolonged indicating more silicon incorporation into the framework. Acidity and phase distribution had an influence on the conversion of 1-butene and selectivity to isobutene. The selectivity to isobutene was higher with catalysts, which contained more SAPO-11 phase. (C) 2003 Elsevier B.V. All rights reserved.