The nanocomposites of poly(vinyl acetate)/montmorillonite (PVAc/MMT) were prepared using vinyl acetate and organically modified alkaline calcium base montmorillonite (MMT) by in situ emulsion copolymerization. The organic modification was acrylic acid including terminal reactive vinylic group. The samples were characterized using fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD). Thermal properties of the PVAc/MMT films were studied by thermogravimetric (TG) and differential scanning calorimetric (DSC). The FT-IR results indicated that the vinyl group on the surface of the vinyl MMT nanoparticles had been successfully copolymerized with vinyl acetate. The XRD results demonstrated that the MMT was exfoliated during polymerization. The exfoliated PVAc/MMT nanocomposites showed a lower glass transition temperature (Tg) and a worse thermal stability compared with the pure PVAc. However, bonding power of the nanocomposite latex of PVAc/MMT was improved due to the strong interaction between silica nanoparticles and polymer matrix via covalent bonds.