Effective dispersion of organically modified montmorillonite-layered silicates in nylon 66 is addressed by synthesizing nanocomposites in situ via interfacial polycondensation from a suspension of silicate platelets in one of the monomer phases using either a stirred or unstirred reactor, while avoiding the detrimental heat history associated with melt compounding of this high melting polymer system. The effects of mixing methodology, reaction conditions, concentration ratio, and clay content are evaluated to elucidate process mechanisms and produce high molecular weight product. Enhanced stiffness of the nanocomposites measured by tensile modulus is related to their nanoscale morphology as characterized by transmission electron microscopy and wide angle X-ray diffraction. POLYM. ENG. SCI., 49:1491-1501, 2009. (C) 2009 Society of Plastics Engineers