Pr(Mg1/2Sn1/2)O3 (PMS) ceramic was prepared through a conventional solid-state reaction method. Crystal structure was investigated through X-ray diffraction (XRD), which certificates that the main phase is PMS with monoclinic P2 1/n1 symmetry. Lattice vibrational modes were obtained through Raman scattering spectroscopy and Fourier transform far-infrared reflection spectroscopy. The Raman spectrum active modes were assigned and illustrated, respectively, and then fitted with Lorentzian function. The four modes within the range of 110-200 cm-1 are derived from the F 2g vibrations (A-site cations), and the other three modes (300-430 cm-1) are derived from the F 2g vibrations (B-site cations).The mode with highest frequency above 650 cm-1 is attributed to A 1g -like mode that corresponds to the symmetric breathing of oxygen octahedral. The far-infrared spectrum with seven infrared active modes was fitted using four-parameter semi-quantum models to calculate intrinsic properties (permittivity and loss). F 2u(2) yielded the greatest contribution to dielectric constant and loss, which is mainly performed as the inverted translational vibration of Pr-MgO6 octahedron.