The microwave eddy current loss in a powder sample has been examined both theoretically and experimentally. It is shown that under certain conditions, the absorption power of the conductive powder inserted in the region of the maximum microwave magnetic field in the cavity is proportional to the bulk conductivity, and therefore the temperature dependence of the bulk conductivity can be easily deduced from experiments on powders. The method is applicable to resistivities ranging from 10−1to 10−6&OHgr; m. Examples of measurements at 9.4 GHz are given for Si, Fe3O4, and VSe2.