The aluminumphosphate designated as meso-ALPO was efficiently coated with 3-n-propylpyridiniumchloride silsesquioxqne polymer, SiPy+Cl-, forming a stable thin film attached to the surface by the Si-O-Al bond. The electroactive species cobalt (II) tetrasulphophthalocyanine complex, CoTspC(4-), was adsorbed on the matrix modified surface, ALPO/SiPy+Cl-, by an ion exchange reaction resulting in a solid designated as ALPO/SiPy+/CoTSpC(4-). The complex showed high affinity of the solid phase and this was not leached off even in contact with 1.0 moll(-1) KCl supporting electrolyte solution, presumably because it was strongly bound to the aluminumphosphate. The experiments revealed that, in the electrooxidation of oxalic acid, electron transfer processes with the metallic center are very fast and that the diffusion process of the acid into the electrode surface is slower. The ALPO/SiPy+/CoTsPc4- system is very stable and sensitive to oxalic acid oxidation. Its linear peak current density changes with concentration change of the oxalic acid up to a detection limit of 1 x 10(-5) moll(-1). The characteristics of the system are suitable for its use as an electrochemical sensor for oxalic acid. (C) 2004 Elsevier B.V. All rights reserved.