Clay-supported platinum catalysts were prepared by ion exchange. The platinum precursor has been reduced either in the presence or in the absence of cinchonidinium cations introduced in the interlamellar space of the cationic clay. The samples were characterized by XRD and TEM. Reduction by NaBH4 in the absence of cinchonidinium cations and the subsequent introduction of this latter ensured the formation of monodispersed, small platinum crystallites immobilized mostly between the clay sheets. On the other hand, reduction in the presence of the organic cations resulted in migration of the platinum particles on the external surface of the clay.