The humidity sensing behavior of a ceramic oxide based on the ZnO-TiO2-Ta2O5 system was analyzed. Samples were uniaxially pressed and sintered at temperature range from 1000 to 1200 degrees C. Electrical impedance and capacitance measurements were realized in different values of relative humidity (from 11 to 100%). The microstructures of the sintered samples were characterized by X-ray diffractions and SEM observations. Mercury porosimetry analyses were carried out to determine the open porosity and the surface area was measured by using the BET nitrogen method. The obtained results were correlated and discussed.