Abstract: A crystalline, galliosilicate molecular sieve having the mordenite structure and the following composition expressed in terms of oxide mole ratios in the anhydrous state:Ga.sub.2 O.sub.3 :xSiO.sub.2 :yM.sub.2 O:tQ.sub.2 Owhere M is an alkali metal, preferably sodium, Q is a quaternary ammonium cation, preferably a benzyltriethylammonium cation, x equals 5.0 to 30, y equals 0.1 to 0.99, preferably 0.40 to 0.90, t equals 0.01 to 0.9, preferably 0.1 to 0.6 and yet equals about 1.0. The crystalline, galliosilicate molecular sieve of the invention may be employed, after reducing its alkali metal content and decomposing Q, as a component of a catalyst which can be used in a variety of chemical conversion processes.