It is recently reported that the preparation of zeolite membranes from clear solutions with low concentrations of Si4+ and Al3+ could prevent secondary nucleation and hence results in tight structures. Therefore. it is essential to study the phenomena of nucleation and crystal growth of zeolites from low concentration and clear solutions. In this study. the dependence of induction periods for nucleation of zeolite A on solution compositions and temperatures was analyzed. The induction periods of nucleation Were found to decrease with the saturation ratios. The dependence of induction periods on saturation ratios was represented by two straight lines and the lines intersected at critical points that corresponded to the points of changing the types of precipitate structures. In the range of the saturation ratio above the critical point, precursors precipitated, while zeolite A precipitated in the rest of the range. This suggests that the induction periods are related to the type of precipitate structures. (C) 2002 Published by Elsevier Science B.V.