Abstract: A process for preparing porous crystalline alumino-silicates consisting of bringing into contact, in an aqueous environment, sodium silicate with an aluminum derivative at a molar SiO.sub.2 /Al.sub.2 O.sub.3 ratio greater than or equal to 8, in the presence of one or more alkaline hydroxides at a molar Me.sup.+ /SiO.sub.2 ratio greater than 0.6, where Me.sup.+ represents the alkaline metal or metals, and in the presence of a mineralizing agent, operating at a temperature of between 20.degree. and 100.degree. C., and controlling the molar OH.sup.- /SiO.sub.2 ratio of the resultant mixture at a value of 0.01 and 0.8, the resultant mixture being crystallized at said molar OH.sup.- /SiO.sub.2 ratio in a closed environment for a period of between some hours and 40 days at a temperature of between 100.degree. and 200.degree. C.