Zirconia (ZrO 2 ) nanoparticles have been prepared by sol–gel route. Low temperature crystallization using base-hot-water treatment (BHWT) was conducted for the sol–gel derived ZrO 2 gel powders at 90°C and at pH 14 for various periods of time. Single phase nanocrystalline tetragonal ZrO 2 (t-ZrO 2 ) was successfully obtained by immersing the dry gel powders into hot, basic condition water and kept at rest for given time. BHWT at pH 14 with sodium hydroxide (NaOH) medium by digestion for 12h and then continuing with stirring for 12h resulted in the formation of t-ZrO 2 with surface area of 292m 2 /g and crystal size of 7nm. Study on base solution medium, using NaOH, shows that the sodium ions play an important role for the formation of t-ZrO 2 by incorporating into the crystal structure during the treatment. BHWT also effectively removed organic groups of the sol–gel derived ZrO 2 nanoparticles.