Abstract: A microwave moisture sensor comprising a first transmission and reception system comprising first transmission and reception horn antennas disposed in confronting relation with respect to each other and with a movable sheet like measurand disposed therebetween; and a second transmission and reception system comprising a second transmission horn antenna for re-emitting a microwave, as received by the first reception horn antenna against the measurand, and a second reception horn antenna for receiving the microwave emitted by the second transmission horn antenna and having passed through the measurand. The antennas disposed on one side of the measurand are spaced from each other by a distance of n.lambda..+-..lambda./4, wherein n is an integer and .lambda. is the wavelength of the microwave, in a direction substantially perpendicular to the plane of the measurand.