Strips of composite membrane, of which one half was the anion exchange membrane and the other half was the anion exchange membrane with polypyrrole layers on both surfaces, when connected to a load resistance, generated an electromotive force (EMF) which was dependent on the relative humidity. The polypyrrole layers acted as an anode active material with the anion exchange membrane acting as a solid polyelectrolyte for anions in the cell. If a linear relationship exists between the EMF and the relative humidity, it can be used as a kind of hygrometer. For the measurements, membranes in the sulfate form were mainly used. The width of the strip was found to affect the maximum EMF and sensitivity to the relative humidity as well as the hysteresis in the EMF with increasing and decreasing relative humidity. (The EMF was 260 mV at 20 MOMEGA load resistance when the strip was 10 mm wide.). In order to examine the effect of the relative humidity on the EMF in detail, samples with restricted water absorption were examined. The relationship between the EMF and relative humidity was fairly reversible in membranes in the sulfate form with low water content, but was irreversible in membranes in the nitrate form. It is thought that water uptake by the anion exchange membrane changed markedly according to the anion species in the membrane.