Precipitated zirconium(IV) hydroxide was ball-milled at room temperature for 1, 3, 9, 35 and 60 h, The samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). DSC curves of the samples, obtained by ball-milling for 1, 3 and 9 h, showed two exothermic peaks due to crystallization of tetragonal ZrO2 as determined by XRD and FT-IR. These two exothermic peaks were ascribed to the heterogeneity of the zirconium(IV) hydroxide structure caused by ball-milling. The samples, obtained by ball-mining for 35 and 60 h, showed only one exothermic peak. Three important phenomena, as a consequence of the ball-milling of zirconium hydroxide, were observed : (a) dehydration, (b) an increase in the activation energy of the crystallization and (c) a decrease in the enthalpy of crystallization of t-ZrO2 from ball-milled zirconium hydroxide, The present study indicated that the process of crystallization of t-ZrO2 from zirconium(IV) hydroxide is more complex than a simple structural (topotactic) rearrangement.