[en] Interest in zirconium as a structural material for nuclear reactors has led to a research for cheaper, more convenient ways of opening up Thai zirconium ores. The most abundant domestic zirconium ore is zircon. Caustic soda was found to be effective in decomposing this ore. The content of zirconium oxide and hafnium oxide in Thai zircon were found to be 65.57+-0.18% and 1.43% respectively by X-ray fluorescence spectrometer. By using a caustic to zircon sand weight ratio of 3:2 and a furnace temperature of 550⁰C for 45 min, the zircon sand was decomposed without previous grinding. It was found that 98.62+-0.23% of the Thai zircon reacted to form water-soluble sodium silicates and water-insoluble sodium zirconates. The contents of zirconium and hafnium oxide in the zirconia sample determined by neutron activation technique were 92.14+-1.86% and 2.53+-0.30% respectively. Quality test of the zirconium crystals done by X-ray diffraction technique found that most of the zirconia crystal structure were monoclinic, some tetragonal form was also present