We have investigated the formation kinetics of nanocrystals from LiTaO3 (LT) glass. The glass sample was prepared by using the polymerized complex method with no addition of a glass former. The thermal characteristics and the structural transformations of pure LT glass have been studied by means of differential scanning calorimetry and in-situ synchrotron X-ray diffraction, and the surface morphology have been studied by using scanning electron microscopy. A temperaturedependent incubation time is observed. After this incubation time, the isothermal kinetics of the crystallization process is described by the Johnson-Mehl-Avrami-Kolmogorov equation, resulting in an Avrami exponent, n, of ∼2.75. The result indicates that the crystallization mechanism is diffusion-controlled growth at an increasing nucleation rate. The effective activation energy deduced from the time of 30 to 50% transformations is 9.2 eV and, based on the relationship ΔEeff = En + bcEg, turns out to arise from the activation energies of 3.3 eV for nucleation and 3.9 eV for growth.