A mordenite (MOR) sample with submicron crystallite size ( 0.1 mum) has been synthesized by hydrothermal transformation of a layered sodium silicate magadiite (Na-magadiite) using tetraethylammonium hydroxide (TEAOH) as an intercalating agent and/or structure directing agent. The MOR sample obtained from Na-magadiite was found, by XRD and N-2 adsorption measurements, to have high crystallinity and high BET surface area. However, the Al-27 MAS NMR spectrum of the calcined MOR sample showed the presence of extra framework octahedrally coordinated aluminum. The catalytic activity of the MOR sample obtained from Na-magadiite was tested for the isopropylation of biphenyl and compared with results obtained with a commercial MOR sample with larger crystallite size (1.0 mum). Both samples showed comparable catalytic activity for the isopropylation of biphenyl, especially at higher temperatures. Under the reaction conditions used, the MOR sample obtained from Na-magadiite showed about 10% lower selectivity for the desired products 4,4'-DIPB and 4-IPBP compared to the commercial MOR sample. Furthermore, unexpectedly, the conversion of 4,4'-DIPB over the MOR sample obtained from Na-magadiite was significantly lower than that of the commercial MOR sample. These differences in catalytic activity might be related to the presence of extra framework octahedrally coordinated aluminum in the MOR sample obtained from Na-magadiite.