Polymethylsilsesquioxane (PMSQ)-montmorillonite (MMT) nanocomposites were prepared by in situ intercalative polymerization. The dispersion of the MMT layers within the matrix was verified by X-ray diffraction and transmission electron microscopy, which revealed an intercalated morphology with layer spacing of 3.42 nm. The layer spacing was not increased after annealing at 150degreesC for 3 h. The reason for this result is explained in light of the molecular structure of PMSQ synthesized in and out of the nanoconfined environment. The coherent order of the silicate layer was decreased after the annealing, possibly because of the change in the PMSQ molecule during the annealing process.