Pyrroloquinoline quinone (PQQ) was immobilized on the silica gel surface modified with zirconium oxide, designated as Si:Zr, by the carboxylic groups of the PQQ molecule and the zirconium oxide on the silica surface. The electrochemistry of PQQ immobilized on the Si:Zr matrix, incorporated in a carbon paste electrode, was evaluated using the cyclic voltammetry technique. The Si:Zr:PQQ-modified electrode showed a redox couple at E m =(E pa1 +E pc )/2=−0.150 V vs SCE at pH 7, close to that observed in aqueous solution, and another oxidation peak, E pa2 =−0.100 V vs SCE. Studies in different pH solutions in the range of 3–7 showed that the first oxidation peak, E pa1 , is highly dependent on the solution pH shifting from to −0.175 to 0.100 V vs SCE, while E pa2 remains practically constant at 0.100 V as the pH decreases from 7 to 3. The immobilized PQQ electrode presented the property to electrocatalyze the NADH at 150 mV vs SCE. The effect of addition of Ca 2+ ions on the electrode electroactivity for the NADH oxidation was also verified. Different from that observed for the PQQ immobilized on other electrode materials, the Ca 2+ ions did not influence the electrocatalytical response; however, the electrode stability was considerably improved in the presence of Ca 2+ ions, indicating that the matrix surface has a great influence on the electrochemical behavior of PQQ.