The present report details the effects of synthesis time, concentrations of hexamethylenetetramine (HMTA) and precursor tin (II) chloride solutions on the self-assembly of SnO2 nanocrystals. High-resolution electron microscopy images revealed that the structures were made of randomly attached SnO2 nanocrystals with sizes in between 2 and 5 nm. X-ray photoelectron spectroscopy (XPS) showed that the Sn3d region was characterized by the spin-orbit splitting of the Sn3d(5/2) ground state at similar to 487.6 eV and by the Sn3d(3/2) excited state at similar to 496.1 eV, which was attributed to the Sn+4 oxidation state of the SnO2 samples. We also found that the self-assembly could be achieved only with aqueous tin (II) chloride solution, and not with aqueous stannic (IV) chloride solution. A plausible growth mechanism is proposed in order to analyze the distinctive self-assembly of SnO2 nanocrystals in the presence of aqueous HMTA solution. (C) 2011 Elsevier Ltd. All rights reserved.