Potassium tantalate film (KT film) having a good humidity detecting property was synthesized at relatively lower temperature such as 100-110°C and a pressure of about 0.1 MPa. KT film has been grown on Ta electrode in aqueous solution of KOH by hydrothermal electrochemical method for a short time. A current source was used to maintain the current density of ImA/cm 2. KT films were fabricated in the concentration range of 2-5mol/L KOH. The film formed on Ta substrate had smooth surface and blue color fabricated in case of the 2mol/L KOH solution used. A porous KT film was formed at the range of 3-4mol/L KOH solution. This film was grown in the shape of islands. At more concentration of 5.0M KOH solution, the film was barely formed. The XRD results showed a specific crystallographic face of the tantalum was reacted preferentially. The thickness on the formed films was evaluated about 5.0μm. In the porous material, water molecule is adsorbed into the capillary pores. As dielectric constant of the water is very high, a capacitance of the porous material increases with humidity. The amount of water absorbed depends upon the pore size. This KT film showed an increase in electrostatic capacity when it was brought into contact with humidity. The capacitance increase versus the relative humidity of the sensor was linear and showed good sensitivity in the lower humidity. The film can be applied as a humidity sensor for gas analysis system.