H-montmorillonite was modified by interlayer surface silylation using 3-aminopropyltriethoxysilane and dodecylamine in ethanol without a pre-swelling step. Dodecylamine acts as a gallery expander and silylation catalyst. The evaporation of ethanol from the dispersion yields well-ordered silylated montmorillonites with large basal spacing between 1.50 and 4.20 nm. Solid-state $^29Si$ CP MAS NMR of the silylated samples showed $Q^2;and;Q^3$ signals as well as $T^2;and;T^3$ signals. The increase in the relative intensity of $Q^3;for;Q^2$ and the appearance of $T^2;and;T^3$ signals was attributed to the grafting of 3-aminopropyltriethoxysilane to the interlayer surface silanol groups.