Abstract ESR spectra and dielectric constant are measured simultaneously for γ-irradiated RbH3 (SeO3)2 and RbD3 (SeO3)2. From the analysis of A tensor of Seb2 radical, it is found that the rotation of SeO3 (II) in RbD3 (SeO3)2 below Tc is quite similar to that in RbH3 (SeO3)2. Meanwhile for RbD3 (SeO3)2 a clear peak of dielectric constant along the a-axis is found at T besides the anomaly along the b-axis.