A micro-particulate aluminosilicate suitable for use as an ion exchanger, adsorbent or the like has a mean particle size of not greater than 3 .mu.m (micrometers), preferably not greater than 1 .mu.m, as measured by precipitation particle size distribution measuring method. The micro-particulate aluminosilicate is produced by a process having the steps of preparing an aqueous solution as a solvent, the aqueous solution containing a water-soluble polymer dissolved therein; adding to the aqueous solution a metal hydroxide or a metal salt, a metal aluminate and colloidal silica as essential components and stirring the mixture to uniformly disperse the essential components so as to form a cake; and synthesizing the micro-particulate aluminosilicate by allowing the cake to mature followed by heating.