Poly(methyl methacrylate)/clay nanocomposites were synthesized via in situ free radical polymerization of methyl methacrylate (MMA) in the presence of functionalized clay. Montmorillonite (MMT), a smectic type of clay, was treated with a commercial cationic surfactant, benzalkonium chloride (BAC), and a synthesized zwitterionic surfactant, octadecyldimethyl betaine (C18DMB). Functionalized MMT was prepared via an ion exchange between Na+ ions in the clay and the surfactant cations in aqueous medium. The intercalation of the surfactant in the clay galleries was determined using X-ray diffraction (XRD). The interlayer spacing for C18DMB was 2.03 nm, higher than 1.86 nm observed for BAC. This is due to longer chain length of C18DMB. Both organophilic clays formed a viscous gel when dispersed in the monomer, MMA. Poly(methyl methacrylate) (PMMA) nanocomposites were obtained by polymerizing the dispersions. XRD and transmission electron microscopy (TEM) indicate predominant exfoliation of the silicate layers in the polymer matrix for MMT treated with C18DMB, and partial exfoliation for MMT treated with BAC.