It was shown that the interrelation between the mean size of AgI nanocrystals prepared in the water pools of reverse micelles as a result of reaction between KI and AgNO3 and the pool diameter has a complex pattern and is determined mainly by the stability of micellar system. Microemulsions with small micelles (the pool diameter is up to 2 nm) are stable due to the presence of micelle oligomeric phase, regardless of the effect of water structurization in pools. In microemulsions with pool diameters from 2 to 6 nm, such an oligomeric phase is absent that leads to the avalanche-like growth of nanocrystals due to their aggregation in organic phase. As the diameter of micelle pools increases above 6 nm, the microemulsions are stabilized because of the limited dimensions of structured water layer and the deceleration of intermicellar exchange. When the excess amount of KI is added to microemulsion, the screening shell of ions is formed around nanocrystals, thus complicating the formation of icelike structure of water in micelle pools.