In this paper, the optical properties of Au-doped rhenium diselenide ( ReSe ₂: Au ) single crystals have been reported. The doping effects of the material were characterized by polarization-dependent transmittance, piezoreflectance (PzR), and photoreflectance (PR) measurements in the temperature range of 15–300 K. The indirect energy gap of ReSe ₂: Au shows a slight redshift with respect to the undoped sample. The low temperature PzR and PR spectra reveal an E₁ ^ex feature at E || b polarization as well as two features, E₂ ^ex and E₃ ^ex , at E ⊥ b polarization. The angular dependence of the excitonic feature amplitudes agrees well with Malus’ law. In comparison with the undoped ReSe ₂ , the excitonic transition energies remain practically unchanged, while the broadening parameter of the excitonic transition features slightly increases due to impurity scattering. In addition, the parameters that describe the temperature variations of the band-edge excitonic transitions were evaluated and discussed.