Polystyrene chains were grown from the surface of synthetic Laponite clay platelets by nitroxide-mediated polymerization (NMP) of styrene using N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] (DEPN) as mediator. A novel water-soluble quaternary ammonium alkoxyamine was first synthesized and intercalated into the clay galleries by cation exchange. Polystyrene chains with controlled molecular weights and narrow polydispersities were then grown from the organoclay. The kinetics of styrene surface NMP polymerizations were investigated and compared with model polymerizations mediated by free alkoxyamine initiator molecules. Both reactions exhibited similar kinetics behaviors indicating that the clay platelets did not affect the livingness of polymerization. The PS-functionalized clay particles were colloidaly stable into toluene, a good solvent for polystyrene, and could be redispersed into tetrahydrofuran (THF) and a series of monomers after drying. Transmission electron microscopy (TEM) analysis of the films cast from the suspensions revealed a fully exfoliated structure of the clay tactoids within the polymer matrix.