The dielectric constants of $(RDA)_{0.69}$ $(ADA)_{0.31}$ mixed crystal were measured along the a- and c-axes in the temperature range from 18 K to 220 K. Below Tg a large dielectric dispersion of both $∈_x(T)$ and $∈_z(T)$ was observed at low frequence below 10 kHz and a large anisotropy in the magnitude of dielectric susceptibility was observed to persist below Tg. $(RDA)_{0.69}(ADA)_{0.31}$ mixed crystal showed the proton-glass phase transition with Tg=36.6K and Tg=32.6K for a- and c-axes respectively, where Tg was defined as corresponding to the maximum peak of the dielectric constant.
