Nanocomposites were prepared by in situ redox intercalative polymerization method, in which alpha-RuCl3 microcrystals were soaked in pyrrole. Polypyrrole (PP) was formed as a result of the intercalation of pyrrole into the layered structure of RuCl3 crystal and the reaction between pyrrole and the host material. The appearance of polypyrrole was proven by infrared spectroscopy. The as-formed (PP)(z+)(RuCl3)(z-) nanocomposites were attached to paraffin-impregnated graphite or gold surfaces and studied by cyclic voltammetry and electrochemical nanogravimetry. The redox behaviour of the composite shows the electrochemical transformations of both the polypyrrole and RuCl3. The redox waves of PP are similar to those observed for very thin PP films. It attests that the response is ofiginated from monolayer-like PP film situated between RuCl3 layers. The transport of the charge-compensating ions reflects the variation of the oxidation states of both PP and RuCl3. The nanocomposites behave as self-doped layers in the potential region when both constituents are charged, i.e., PP is partially oxidized while RuCl3 is partially reduced, since the electroneutrality is assured by mutual charge compensation. When PP is reduced, cations enter the layer to counterbalance the negative charge resulted from the reduction of Ru(III) to Ru(II). It was also found that the intercalation of water molecules is - albeit still substantial - smaller than that of pure RuCl3 microcrystals which is related to the presence of PP between the RuCl3 layers. (c) 2007 Elsevier Ltd. All rights reserved.