The (RbBi)1/2MoO4 ceramic was prepared via solid state reaction method. The room temperature far-infrared reflectivity spectra were measured and 15 vibration modes were observed. Kramers-Kronig (K-K) relationship was employed to fit infrared spectra. The optical frequency permittivity ε∞ is equal to 2.17 for the dielectric materials, and the extrapolated value to microwave frequency (at about 9 GHz) is 20.56 and it is slightly smaller than the actual measured value ~21.4. The calculated value of quality factor (Q×f) is 11 790 GHz, which is higher than the actual measured value ~6 200 GHz, and it can be deduced that the quality factor of the (RbBi)1/2MoO4 ceramic material has large room for improvement.