A series of superabsorbent composites containing Montmorillonite (MMT), modified- Montmorillonite (OMMT) and sodium acrylate were synthesized by free-radical polymerization in aqueous solution. The structure of composites was characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and X-ray diffraction (XRD), and the results showed that the polymer chains were grafted onto the edge and the surface of MMT or OMMT. At the same time, the equilibrium swelling ratio of the composites was investigated as a function of the clay content and the results showed that the equilibrium swelling ratio of composites was improved by the introduction of clay. The maximum equilibrium swelling ratio of composite in distilled water and 0.9 wt% sodium chloride solutions were up to 2450 g/g and 118 g/g, respectively. Finally, the result of thermogravimetric analysis (TGA) suggested that the introduction of clay and modified clay could improve the thermal stability of superabsorbent composites.