An exfoliated clay−polymer nanocomposite was prepared by surface-initiated ring opening metathesis polymerization (SI-ROMP) of norbornene on a montmorillonite (MMT) clay with a modified surface. Utilizing the hydrothermal-silylation reaction between a norbornenyl-bearing chlorosilane agent and silanol groups of the MMT clay, we were able to bind a metal alkylidene catalyst to the surface in order to grow poly(norbornene) chains directly from the surface using ROMP. Our approach produced nanocomposites having poly(norbornene) chains that are covalently attached to the inorganic substrate, as opposed to most conventional polymer-clay composites that have ionically tethered chains (via the ammonium-based modifiers of the organoclay) or physically adsorbed polymers. POLYM. ENG. SCI., 55:2349–2354, 2015. © 2015 Society of Plastics Engineers