The creation of new composite materials with specified radio-frequency properties is often carried out using small-sized inclusions, while the polarizability parameters of these small bodies in electric and magnetic fields play a significant role. The paper considers the possibility of measuring the polarizability of small components of the composite in an open quasi-optical resonator. It is shown that the values of the electric and magnetic polarizability of small particles can be estimated from the shifts of the resonant frequencies that arise when a small scatterer is placed in the resonator.