Abstract: A humidity sensor utilizing the electrical output of a piezoelectric crystal held in compressive stress at one end of a lever arm, the fulcrum at the other end of the lever arm consisting of a flexure hinge of moisture sensitive material with a thickness under 10 mils. The crystal is nested in a frame to which the flexure hinge is attached and the frame hinge and lever arm may be molded out of the same moisture sensitive material. A moisture sensitive form of Nylon may be used for the flexure hinge. The signal output of the crystal is a function of the compressive stress which in turn varies as the modulus of the flexure hinge varies as caused by changes in ambient humidity.