A finely divided zeolite powder of high flowability is provided. This zeolite powder is represented by the formula: Na.sub.2 O.Al.sub.2 O.sub.3.nSiO.sub.2.wH.sub.2 O (n=1.8.about.3.0 and w=1.about.6) and comprises at least 99 weight % of particles having a particle size of 1-5 microns and has an aerated bulk density of from 0.3 to about 0.5 g/cc, a degree of cohesiveness of not larger than 56%, and a general flow index (expressed as the sum of indexes of the repose angle, spatula angle, compressibility and degree of cohesiveness) of from 30 to about 50. The zeolite powder is prepared by adding an alkali metal aluminate to an aqueous zeolite slurry containing 3052 wt. % of zeolite (an anhydride) and having pH of not higher than 12.8; adjusting the pH of the slurry to a value not higher than 11; and then, drying the slurry. The zeolite powder is useful as a builder for detergent.