A new water permeability sensor based on the sensitivity of polyimide to humidity has been fabricated for the measurement of the water penetration of thin metal films. To evaluate the sensitivity of the polyimide layer a special humidity sensor was also fabricated. This humidity sensor demonstrates good linearity, a relatively fast response time (1.5-2 min), and good sensitivity. To evaluate the permeability sensor a 5000 AA gold film with a pinhole density of approximately 100 per cm² was measured. The results show a capacity change from 100 to 109 pF and saturation after 300 h.