Utilizing titanyl sulfate as a TiO2 source, via a novel synthesis method—the detonation method—nanosizedTiO2(n-TiO2) powders were prepared. The results showed that the as-preparedn-TiO2 powders did not have enough time to grow into large and fine crystallites, and that thecharacteristics of high temperature, high pressure and high cooling were helpful in the synthesisof nanosized materials. The anatase phase appeared to be the stable form of nanocrystallineTiO2 at small crystallite sizes to some extent and part of the rutile phase couldtransform to the anatase phase when the detonation products were oxidizedto eliminate the impurities via the combined action of chromic anhydride(CrO3) and concentrated nitric acid. The main reason resulting in the reversal of stability ofanatase and rutile could be the differences in the surface energy of anatase and rutile atsmall crystallite sizes.