13C CP MAS NMR and 29Si MAS NMR were used to characterize silylated montmorillonites and to estimate the extent of the silylation reaction. Indirectly-detected proton relaxation times of the intercalated surfactant were measured in both silylated and non-silylated clay systems to monitor the dynamics of intercalated species. A greater degree of mobility in the silylated montmorillonites was found. The lack of NMR information resulting from paramagnetic interaction brought about by structural Fe(III) ions was considered. The resulting broadening can prevent the estimation of the trans/gauche conformer ratio of the intercalated surfactant alkyl chain.