A theoretical study of the infrared transmission spectra of the GaS films is carried out by taking into account an anisotropy of the layered GaS crystals. It is shown that the calculated transmission spectra T(nu) agree well with the experimental ones reported by Abdullaev and Ibragimov [A.G. Abdullaev, T.D. Ibragimov, Fiz. Tverd. Tela, 28, (1986), 2545]. The intensive peak at the frequency nu = 296 cm(-1) is related to the absorption of p-polarized light by the transverse optical phonon mode with nu = nu(T)(perpendicular to C) (the C axis of highest symmetry is perpendicular to the cleavage plane of the crystal) and the surface mode which frequency is close to nu(T)(perpendicular to C). The other peak at nu = 336 cm(-1) is relatively weak due to the absorption by the surface mode with nu approximate to nu(L)(parallel to C) only.