[en] The electronic structures, the magnetic moments and the optical conductivity spectra of the Co_1-xAl_x (x=0.5, 0.4375, and 0.375) alloys were calculated using the tight-binding linearized-muffin-tin-orbital method. The supercell method was employed to calculate the properties of the alloys with the off-stoichiometric concentrations. The calculated magnetic moments were in reasonable agreement with the experimental results. The inclusion of corrections for both the real and the imaginary parts of the self-energy markedly improved the agreement between the experimental and calculated the optical conductivity spectra