Encapsulation of inorganic nano particles (as a core) by polymers (as a shell) is one of the interesting research subjects that lead to the synthesis of nano composite Some of the preparative methods for the synthesis of nano composite are dispersion suspension emulsion and mini-emulsion polymerization techniques Here core-shell nano composite particles of poly (styrene-co-methyl acrylate) and bentonite (modified with octadecyl amine) were prepared by mini-emulsion polymerization The mini-emulsions were prepared by dispersing bentonite in the monomers mixture (styrene and methyl acrylate) in the presence of sodium dodecyl benzene sulfate (SDBS) and Span-60 as surfactants and hexadecane as costabilizer using ultra sonication The stability of both mini-emulsion and the obtained latex depends on premixing procedures time of ultrasonication and more importantly on the applied surfactants The encapsulation of the nano clay was confirmed by FTIR and XRD analysis The morphology of the nano composite particles was determined by SEM and TEM analysis TGA analysis of the composite particles shows that they exhibit better thermal stability as compared to the pristine polymer (C) 2010 Elsevier B V All rights reserved