Polarized IR reflectance spectra of eight Tutton salts single crystals: M′ 2M″(SO 4) 2·6H 2O; M′: K + or NH 4 +; M″: Ni 2+, Co 2+, Zn 2+ or Mg 2+) were recorded at near-normal incidence. Dispersion analysis was performed for the whole mid-IR region. The results on ν 3(SO 4 2−) frequency region are reported in this paper. Reflectance spectra were recorded using radiation with polarization along the b crystallographic axis and in the ac crystal plane. Results of the fit for the transversal frequency, oscillator strength, attenuation constant and the orientation of the transition moments in the ac crystal plane for the ν 3(SO 4 2−) frequency region are presented. The longitudinal frequencies for the A u vibrations were obtained from the energy-loss function spectra, while for the B u vibrations a particular approximation was used. In addition to frequency values, the directions of the longitudinal transition dipole moments in the ac crystal plane were also found. The dependence of the principal axes of the real and the imaginary parts of the dielectric tensor, on the radiation frequency, was established. An attempt was made to estimate the transition moment directions of the ν 3(SO 4 2−) mode components by correlation of the spectroscopic and structural findings.