o-Phenylene diamine molecules were intercalated into molybdenum oxide layers by an in situ co-precipitation method. The structure and composition of the intercalated material were studied by X-ray diffraction (XRD), infrared spectroscopy (IR) and elemental analysis. XRD data evidenced a layered structure with a spacing of 18 angstrom, which corresponds to an organic-inorganic hybrid-layered structure. IR and UV-vis spectra indicated the polymerization of o-phenylene between the molybdenum oxide layers. It was also observed that compared with aniline molecules, o-phenylene diamine molecules can be selectively intercalated into molybdenum oxide layers. We provide evidence that affinity for o-phenylene diamine to form intermolecular polymers is the reason for its selective intercalation. The polymer chain structure of o-phenylene diamine makes it a preferential guest species compared with aniline. We believe that this opens a new way to create organic-inorganic hybrid structures. (C) 2008 Elsevier Ltd. All rights reserved.