the present invention relates to a process for the synthesis of ato molecular sieve framework comprising forming a reaction medium comprising of reactive sources al 2 o 3 , p 2 o 5 and / or silica and a templating agent and subjecting the reaction medium to microwave hydrothermal heating until crystals of ato framework are formed . the templating agent used in the reaction medium is a long chain quaternary ammonium dihydroxide organic moiety having c 5 - c 10 linear chain alkane , alkene or alkyl . the crystalline ato type molecular sieve framework obtained by the process of the present invention is pure and completely free from commonly observed major impurity phase , namely ael framework .