Formation of sol solutions is intrinsically a non-equilibrium phenomenon governed by a competition between kinetics and thermodynamics. This Letter investigates the aggregation behavior of sols in early formation process through monitoring microstructures of sols experimentally. Two kinds of aggregation structures and a dynamic feedback disaggregation structure evolution were found determined by reflux time through the particles' sticking probability. It can be deduced that the clusters/aggregations were formed through a process of nucleation, ramous growth and disaggregation. Moreover, it was shown that the initial concentration had no effects on the structure or size of clusters. (C) 2010 Elsevier B.V. All rights reserved.