Poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)/clay nanocomposite (PMMA/OBT) were successfully prepared in dioxan at room temperature via in situ radical polymerization initiated by a new Ni(II)alpha- Benzoinoxime complex as a single component in presence of 3% by weight of an organically modified bentonite (OBT) (originated from Maghnia, Algeria) and characterized by FTIR, H-1-NMR and viscometry. Mainly intercalated and partially exfoliated PMMA/OBT nanocomposite was elaborated and evidenced by X-Ray diffraction (XRD) and transmission electron microscopy (TEM). The intrinsic viscosity of PMMA/OBT nanocomposite is much higher than the one of pure PMMA prepared under the same conditions. Differential scanning calorimetry (DSC) displayed an increase of 10 degrees C in the glass transition temperature of the elaborated PMMA/OBT nanocomposite relative to the one of pure PMMA. Moreover, the TGA analysis confirms a significant improvement of the thermal stability of PMMA/OBT nanocomposite compared to virgin PMMA: the onset degradation temperature of the nanocomposite, carried out under nitrogen atmosphere, increased by more than 45 degrees C. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3227-3233, 2011