Highly ordered Ba(Mg1/3Nb2/3)O-3 ceramics from hydrothermal powders were investigated for the first time using infrared spectroscopy. The experimental data were analyzed in view of the 16 predicted modes of the trigonal structure and adjusted by a four-parameter semiquantum model. The obtained phonon parameters allowed us to calculate the real part of the dielectric permittivity and losses in all infrared regions, and also to estimate the quality factor (Q) for this material in the microwave region. The values obtained for the dielectric Permittivity (epsilon' = 19) and Q (12 800 at 10 GHz) showed that hydrothermal Ba(Mg1/3Nb2/3)O-3 ceramics are good materials for passive components in microwave circuits.