Polarized IR reflectance spectra of monoclinic single crystal ~-Bi20 ~ for different directions of the wave vector k and the electric field E of the incident radiation have been measured in a wide temperature range (25-400 K). A significant dependence of the spectrum shape on the direction of the vector E within the ac-plane was observed. Frequencies, strengths, widths and polarizations of the TO modes were restored using the Lorentz dispersion model extended for the monoclinic crystal lattice. Remarkable distinction between intensities of Au-and B=-modes is observed.