Polytetrahydrofuran (PTHF)/clay nanocomposites were prepared by two routes: in situ cationic ring opening polymerization (CROP) and a method involving "click" chemistry. In the first method, PTHF chains were grown from the surface of the organo-modified montmorillonite clay by CROP of tetrahydrofuran (THF) through the hydroxyl functions of the clay by using trifluoromethanesulfonic anhydride, in the presence of 2,6-di-tert-butylpyridine as proton trap and dichloromethane as solvent. The polymerizations were affected by the clay content ratios. The living characteristics of the polymerization were demonstrated by the semilogarithmic first order kinetic plot. In the second method, CROP of THF has been performed independently to produce alkyne-functionalized PTHF and the obtained polymers were subsequently anchored to azide-modified clay layers by a "click" reaction. The exfoliated polymer/clay nanocomposites obtained by both methods were characterized and compared by X-ray diffraction spectroscopy, thermogravimetric analysis, and transmission electron microscopy. Compared to the virgin polymer, the nanocomposites exhibited improved thermal stabilities regardless of the preparation method. However, the nanocomposites prepared by the "click" chemistry approach appeared to be thermally more stable than those prepared by in situ polymerization. Moreover, the "click" chemistry method also provided better exfoliation.