Nanocrystalline ZrO₂ powder was synthesized by dc transferred arc thermal plasma reactor by homogeneous gas phase condensation mechanism. ZrO₂ is an oxide ceramic with a high melting point, good chemical resistance and high mechanical strength. When doped with certain oxides, ZrO₂ shows high ionic conductivity. ZrO₂ is also recognized as a superior thermal barrier material. Thermal plasma synthesis of oxide nano materials shows pressure dependent crystalline phase and crystallite size. The X-ray diffraction analysis clearly shows that as the ambient oxygen gas pressure increases from 100 Torr to 1000 Torr the abundance of tetragonal phase goes on increasing. The morphology of the as synthesized ZrO₂ powder was found to be spherical and independent on the ambient gas pressure as seen from the Scanning Electron Microscopy studies. The specific surface area of powder was calculated using the nitrogen gas adsorption Brunauer, Emmett, Teller surface area analysis technique and found no much variation.