Syliation of sodium montmorillonite (Na-MMT) was performed using different concentrations of -aminopropyltriethoxysilane (-APTES) in water as dispersing medium for optimizing the appropriate amount of the modifier. The amount of (1) intercalated silane and (2) Chemically grafted onto the clay was calculated based on Thermogravimetric analysis (TGA) analysis. Moreover, TGA results showed the success of clay modification, the modified clay showed better thermal properties. Furthermore, Fourier transform infrared spectroscopy (FTIR) also confirmed the successful chemical grafting of silane, by arising of new N-H bending peak at around 700 cm-1. 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy showed the characteristic peak assigned for formation of T2 or T3 supporting the success of grafting process. The gallery spacing was evaluated by X-ray diffraction, which expressed enhancement of d-spacing with silane modification. These clay materials are used for polymer nanocomposites.