Optical properties and lattice dynamics of hexagonal 2H-BaMnO 3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be E g = 3.2 eV. At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons, two of them are polarized along the c-axis and four are polarized within the a−b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complimentary density functional theory lattice dynamics calculations are consistent with the 2H-BaMnO 3 structure belonging to the polar P6 3 mc space group at room temperature. All observed vibrational modes are assigned to the specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below T C =130±5 K, which is accompanied by the lattice symmetry change from the P6 3 mc to the P6 3 cm. Simultaneously, at temperatures below T C several additional IR-and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with appearance of the electrical polarization along the c-axis and a previously known tripling of the primitive cell volume at low temperatures. PACS number(s): 63.20.dh, 75.47.Lx, 75.85.+t