[en] As considerable progress is expected to result from the use of high-T/sub c/ superconductors at microwave frequencies, we started a study of the microwave properties of Nb₃Sn. Preparation was done by exposing niobium cavities to a saturated tin atmosphere. Microwave measurements of the unloaded quality factor Q₀ and the critical flux density B/sup ac//sub c/ were performed in the TE/sub 011/ mode at 9.5 GHz. At 1.5 K low-field values of Q₀ up to 6 x 10⁹ and B/sup ac//sub c/ values up to 100 mT with a Q₀ of 2.3 x 10⁹ were obtained. At 4.2 K and at low magnetic flux densities a Q₀ of 2.7 x 10⁹ was reached