This paper deals with the crystallization pathway of tin dioxide ultra-small nanoparticles synthesized via a nonaqueous sol-gel route based on the etherolysis of tin tetrachloride (SnCl 4) precursor. Two different ethers were used as oxygen donors: diisopropyl ether (i Pr 2 O) and dibenzyl ether (Bn 2 O). The solvothermal treatments of SnCl 4 in i Pr 2 O at different temperatures and reaction times, revealed in the early stages of the reaction the formation of an organic polymeric phase in which crystalline nanoparticles are embedded. In the case of the SnCl 4-Bn 2 O system, the formation of a brownish polymer containing crystalline oxidic nanoparticles and the production of water were evidenced. With both ethers, an unexpected intermediate disordered nano-crystalline phase is formed, which progressively transforms into rutile-type SnO 2 nanoparticles. The formation of the polymeric phase, which is suspected to act as a trap for the nanoparticles, freezes the intermediate phase, limits the particle growth and delays the restructuration into the rutile-type structure. The