Three different loading of 3-aminopropyltriethoxysilane (APS) was used to modify the Na-montmorillonite via cation exchange technique. The Na-MMT and silane-treated montmorillonite (STMMT) were melt-compounded with polycarbonate (PC) by using Haake Minilab machine. The PC nanocomposite samples were prepared by using Haake Minijet injection molding technique. The intercalation and exfoliation of the PC/MMT nanocomposites were characterized by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal properties of the PC nanocomposites were investigated by using dynamic mechanical analyzer and thermogravimetry analyzer. XRD and TEM results revealed partial intercalation and exfoliation of STMMT in PC matrix. Increase of APS concentration significantly enhanced the storage modulus (E') and improved the thermal stability of PC nanocomposites. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3967-3975, 2009