Abstract: The feasibility of transforming palygorskite from two localities to smectite hydrothermally at temperatures ranging from 22° to 160°C was investigated in a series of laboratory experiments, in which alkalinity was maintained in the pH range of 11.4 to 12 by adding NaOH. The smectite formed was characterized by chemical, spectroscopic, and electron microscopic techniques. Smectite formed rapidly at > 100°C; the transformation was slow, however, at 22°C. The introduction of MgCO3 accelerated the alteration process, but changes in alkalinity at pH > 12 and the difference in elemental composition of the palygorskite samples did not significantly affect the alteration. A pressure of one atmosphere and a temperature of 22°C were sufficient for some transformation to occur within a few months, provided the alkalinity was maintained close to pH 12. X-ray powder diffraction characterization of the product indicated a smectite, and infrared spectroscopy indicated saponite. The alteration to smectite was appreciable even at room temperature, which suggests that the reaction can take place without any external heating.