The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample (kaolinite + water), and time of treatment. As a consequence of this particle-size reduction the surface area increases sharply with the sonication time from 8.5 to 83 m2/g after 20 h with the most energetic treatment. Contrary to what is observed in the grinding treatment, sonication did not cause the amorphization of kaolinite, as observed by XRD and FTIR data. Nevertheless, ultrasound treatment increased the structural disorder, which consisted in increases in the proportion of specific translations (-a/3+b/3) between adjacent layers in the first hours of treatment, followed by increases in the proportion of random translations between layers.