[en] Results of Moessbauer, magnetic and X-ray diffraction measurements of Fe_3-xCo_xAl system are presented. At small concentration of Co the structure is of DO₃-type. For x=0.5, Fe_3-xCo_xAl is located on the ternary Fe-Co-Al phase diagram in the region where two crystallographic phases coexists. It is shown how the presence of Co modifies the lattice parameter and the Debye temperature. Dependence of these two parameters on x are discussed and qualitatively explained as due to the lattice shrinking caused by Co-Al pair interaction. The magnetic moment of Co is estimated to be approximately equal to 0.5 μ_B at x=0.0 and 1.1 μ_B at x=2.0. The magnetic moment of Fe seems constant and equal to approximately 1.9 μ_B for x<1 and increases to 2.7 μ_B at x=2.0. Dependence of the average isomer shift on x and presence of one component only in the spectrum of FeCo₂Al indicate that Co locates preferentially at (A,C) sites which could have been expected based on earlier data. It is shown that a simple model of the disorder described by the binomial distribution and linear dependence of the hyperfine field of impurity atoms in the nearest neighbourhood is not adequate for description of the observed hyperfine magnetic field distribution