A method for making an organometallic treated molecular sieve is described in which a molecular sieve having at least one hydroxyl group and at least [AlO.sub.2] and [PO.sub.2] tetrahedral units and having an average pore dimension less than or equal to about 5 .ANG. is contacted with a solution comprising an organometallic compound and a non-proton donating solvent. The resulting organometallic treated molecular sieve has enhanced ethylene and/or propylene selectivity when used in the conversion of organic oxygenates to olefins. The ethylene and/or propylene selectivity, as well as catalyst life, are further enhanced when the resulting organometallic treated molecular sieve is combined with an oxide of at least one metal selected from Groups 2, 3 and Group 4 of the Periodic Table.