The invention relates to a method and a device for measuring the temperature of a body by means of microwaves. It consists in measuring the signals of the thermal noise which is emitted by a volume of this body which is covered by a probe. In this process, a measurement against ZERO is carried out by introducing into the measuring line signals of an auxiliary noise source having a power that is variable and calibrated with respect to temperature, by connecting the measuring line cyclically to the probe and shortcircuiting it, and varying the power of the auxiliary noise source until the integrated signal returns to a receiver on ZERO.