Tin oxide nanoparticles of uniform size with around 5 nm distribution were synthesized in the aqueous solution of stannous chloride under an oxidizing environment. The syntheses were carried out with Cobalt-60 gamma radiation in N₂O saturated solution, photoirradiation using 300 nm UV lamps as well as normal chemical route in the presence of H₂O₂ at room temperature under ambient laboratory conditions. The nanoparticles were characterized by XRD, FTIR and Raman spectroscopy, SEM and HRTEM measurements. The synthesis mechanism was investigated through the electron pulse radiolysis studies. It was established that the formation of tin oxide nanoparticles takes place only through the reactions of oxidizing free radicals like OH^• or Cl₂^•- with Sn²⁺ ions in aqueous solution. The formation of tin oxide was found follow similar pathways in all the three cases, except that it took a longer time in the case of normal chemical route as compared to the other two routes. The size and shapes of the nanoparticles were found to be identical in all these three cases.