A nanocomposite possessing perovskite-related nanosheets dispersed in a siloxane network was prepared by cohydrolysis of the n-decoxy derivative of an ion-exchangeable layered perovskite, HCa2Nb3O10·xH2O (HCaNb), and tetramethoxysilane (TMOS) via a sol–gel process involving exfoliation. In the X-ray diffraction (XRD) pattern of the product after drying for 1 d, the (0 0 l) reflections disappeared. The transmission electron microscopy (TEM) image of the product after drying for 1 d showed dark lines with a thickness of 1.5 nm, which was consistent with the thickness of an individual nanosheet, indicating exfoliation of HCaNb. In the XRD patterns of the reaction products of the n-decoxy derivative of HCaNb and TMOS before drying and after drying for 60 min, (0 0 l) reflections were detected. After drying for 80 min, the intensity of the (0 0 l) reflections decreased. The intensity decreased with an increase in the drying time, indicating that the exfoliation of HCaNb occurred during the drying process.