A process for preparing a beta zeolite is described, comprising at least the following steps: i) mixing, in an aqueous medium, at least one source of at least one tetravalent element X, at least one source of fluoride anions and at least one quaternary ammonium salt with formula (H.sub.3C).sub.2--N.sup.+--(CH.sub.2CH.sub.2C(CH.sub.3).sub.3).sub.2; ii) treating said mixture hydrothermally until said beta zeolite is formed.