The electronic structures of ordered Ni 3 Al 1 - x Mn x alloy were calculated using the ab inito self-consistent linear muffin-tin orbital (LMTO) method with the local density approximation. Two models of the site occupancy in the elemental f.c.c. cell were considered: (A) Mn atoms substituting the Al atoms located at the corners of the f.c.c. cube; (B) Mn atoms substituting the Ni atoms located at the faces of the cube while maintaining the appropriate number of Ni atoms at the cube corners. LMTO-atomic spherical potential approximation calculations were performed for x=0, 0.25, 0.50, 075, 1.0 and compared with measured X-ray absorption spectra. The influence of manganese atoms location in the f.c.c. lattice on the density of state (DOS) shapes was discussed. The performed studies indicate that it is more features in the DOS resulting from the second model of Mn substitution that find confirmation in the X-ray absorption spectra.