ZnO nanocrystals were synthesized as a case study of a novel, general method for the preparation of nanocrystalline oxides. ZnO sols were injected into a solution of diphenyl ether and dodecylamine heated at 160 °C, followed by heating for 1 h and further extraction and purification of the product. The key point in the preparation of the ZnO sol was the hindering of the condensation reactions, by complexing the Zn ions by acetylacetone before adding an ammonia solution. The ZnO grain size could be controlled by changing the amine concentration and the sol processing. Evidence is presented for a double role of dodecylamine, as an inorganic condensation catalyst and also as a growth regulator.