Two polymerizable cationic surfactants, vinylbenzyl n-alkyldimethyl (n = 12 or 18) ammonium chlorides, were used for functionalization of montmorillonite (MMT) and preparation of unsaturated polyester (UP)-clay nanocomposites. Polymerizable organophilic clays were prepared by exchanging the sodium ions of MMT with vinylbenzyldodecyldimethyl ammonium chloride (VDAC) or vinylbenzyloctadecyldimethyl ammonium chloride (VOAC) in an aqueous medium. The dispersion of organoclays in UP led to gel formation. UP/VDAC-MMT resulted in intercalated nanocomposites while UP/VOAC-MMT formed partially exfoliated nanocomposites. nanocomposites exhibited higher dynamic modulus than pristine UP.