SAPO-34 molecular sieves have been synthesized with different structure directing agents. Although materials with the same framework structure (CHA type) are obtained in all cases, they possess different physicochemical properties, especially textural parameters and crystal size. These catalysts have been tested in the MTO process. All the samples exhibited high activity and selectivity to short chain olefins at the initial stages of the reaction, but they deactivate rapidly with time on stream, especially at high space velocity. It has been observed an important influence of the external surface, crystal size and acidity on the activity, selectivity and lifetime of the different samples. Thus, the sample synthesized with tetraethylammonium hydroxide as structure directing agent rendered the best catalytic performance owing to its higher external surface, smaller crystal size and higher acidity. (C) 2011 Elsevier B.V. All rights reserved.