  We have investigated the microwave non-reciprocity for a non-centrosymmetric
antiferromagnet Ba$_2$MnGe$_2$O$_7$. The magnon modes expected by the
conventional spin wave theory for staggered antiferromagnets are certainly
observed. The magnitudes of exchange interaction and magnetic anisotropy are
obtained by the comparison with the theory. The microwave non-reciprocity is
identified for one of these mode. The relative magnitude of microwave
non-reciprocity can be explained with use of spin wave theory and Kubo formula.
