We report the calculated structural, electronic, and optical properties of antimony triiodide (SbI3) in the rhombohedral structure of 148 (R-3) space group. All the calculations were carried out using full-potential linearized augmented plane wave method with (TB-mBJ) exchange–correlation functional within the framework of density functional theory (DFT) provided in WIEN2k. The calculated ground state lattice parameters and atomic positions match reasonably well with the available experimental data. The calculation of electronic band structure and density of states shows that SbI3 has an indirect band gap of 2.49 eV. Density of States reveals that the conduction band and valence bands are mainly contributed by p-states of antimony and p-states of iodine atoms, respectively. We have observed the optical anisotropy in various optical properties, viz., absorption coefficient, refractive index, extinction coefficient, etc. along xx and zz directions. The absorption coefficient along xx indicates two excitonic absorptions, a stronger one at 2.79 eV and a weaker one at 3.33 eV.