Clay membrane hybrid composites were prepared by facile solution-casting of aqueous precursor suspensions of poly(vinyl alcohol) (PVOH) and montmorillonite clay (MMT), then cross-linked by gamma irradiation. The influences of absorbed dose and polymer loading on composite structure and properties were investigated. A moderate amount of PVOH (P4C6) is found to be optimum for fabricating mechanically strong PVOH composites; however, gamma irradiation has a positive influence on strengthening composites only with low PVOH content. Scanning electron microscopy (SEM) observation shows a layered structure from the cross-section of a cryo-fractured surface for all composites, and a comparatively smooth surface. The wide-angle X-ray diffraction (WAXD) characterization shows an intercalated MMT structure with incorporation of PVOH. Cross-linking and the increase of clay content lead to a decreased onset decomposition temperature but an increase in the temperature at the maximum decomposition rate and enhancement of the residue of the resulting materials. The clay membranes possess very low flammability, which is not significantly influenced by gamma irradiation.