Experimental techniques for measuring the magnetic susceptibility tensor components in microwave cavities are described. General expressions for the perturbation of microwave cavities by the magnetic properties of ferrites are developed. Experimental results are given for Ferramic 1331 measured at 9165 Mcps. Since these results indicate that both the real and imaginary parts of the tensor components &khgr; and &kgr; are approximately equal to each other in the resonance region, only measurement of the diagonal components may suffice to specify the complete tensor. However, whenever the small differences between &khgr; and &kgr; are desired, measurement of the tensor susceptibility in a degenerate cavity will be necessary. An attempt has been made to compare the experimental results with the Bloch‐Bloembergen magnetic resonance theory as applied to circularly polarized excitation.