The interaction between zirconia and polyethyleneimine (PEI) has been characterized using Fourier transform infrared analysis (FTIR) and X-ray photoelectron spectroscopy (XPS). For FTIR, polyvinylimidazole with an aromatic amine group and tetraethylenepentamine were added for an in-depth study: two new broad bands due to nitrogen coordinated with zirconium are seen in the 1580-1560 cm(-1) region and 1450-1350 cm(-1) region, respectively. XPS shows that both ZrOH and N+ were involved in a minor part: only, in good accordance with FTIR. After a cross-linking step of the adsorbed PEI on zirconia, a ratio of about one molecule of cross-linker to five PEI units was obtained by both methods. From XPS Zr 3d signal attenuation, the PEI thickness on plates is about 1.2 and 3.5 nm before and after the cross-linking step, respectively; the cross-linked PEI thickness on zirconia membrane is larger because of the procedure of coating or porous and tubular character of membranes.