Terahertz time-domain spectroscopy has been used to study the optical properties of Pr³⁺-doped selenide glasses. The complex refractive indexes of Pr³⁺-selenide glasses were measured in a frequency range from 0.3 to 1.5 THz. The real and imaginary refractive indexes increased with increasing frequency and Pr³⁺ ion concentration. The obtained result indicated that the phonon modes of the Pr³⁺-doped selenide glasses shift to lower frequencies with the concentration of Pr³⁺ ions. The theory of far-infrared absorption in amorphous materials was used to analyze the results. The measured data showed that the disorder-induced terahertz absorption increased with increasing Pr³⁺ ion concentration.