[en] The optical conductivity spectra of the Ni₃Al alloy were measured by using spectroscopic ellipsometry in the energy range of 0.5-4.7 eV at 20 and 293 K. All the spectra showed two prominent peaks, one in the ultraviolet region(around 4.3 eV) and the other in the infrared region (around 0.9 eV). As the temperature decreased, the magnitude of the optical conductivity decreased owing to a reduction in the Drude contributions. The two peaks were also slightly blue shifted because of thermal contraction. The electronic band structures were calculated using the linear-muffin-tin-orbitals method within the local-(spin)-density approximation. Both the paramagnetic and the ferromagnetic phases were calculated. The calculated magnetic moment was 0.60 μ_B per unit cell. The optical conductivity spetra were also calculated and the calculated spectra exhibited a close agreement with the experimental ones provided that an energy-dependent Lorentzian broadening and the so-called λ-fitting were applied to the calculated spectra. The electronic transitions between the Ni d bands and/or the Ni d bands hybridized with Ni and Al sp characteristics are responsible for the two peaks