New hybrid inorganic-organic nanocomposite systems have been obtained by intercalation of polyethyleneimine (PEI, 5 x 10(4) Da) into alpha- and gamma-structured zirconium phosphates. The composites can be formulated as alpha-Zr(HPO4)(2) . 2.7(PEI). 1.8H(2)O and gamma-Zr(PO4)(H2PO4). 1.03(PEI). 3.3H(2)O, when dried at room temperature and 75% RH. The corresponding interlayer distances are 2.0 and 2.5 nm, respectively. The ac conductivity of the gamma-nanocomposite at 100 degrees C and 82% RH, is significantly higher (2.6 x 10(-5) S/cm) than that of the alpha-intercalate (4.8 x 10(-7) S/cm). Vibrational spectroscopies (IR and incoherent inelastic neutron scattering) have shown that increasing the temperature induces progressive proton transfer from the host layer surfaces to the guest, with successive formation of protonated NH2+ and NH3+ groups (arising from secondary and primary amine groups respectively). Proton transfer is, however, more complete in alpha-ZrP-PEI.