A1As(y)Sb(1-y) and InAsySb1-y ternaries have been grown by Molecular Beam Epitaxy on (001) GaAs and (001) InAs substrates. Growth parameters and composition of the layers were determined by reflection high-energy electron diffraction and single-crystal X-ray diffraction measurements, respectively. The compositional dependence of AlAsySb1-y and InAsySb1-y on the ratio of Sb-4 to As-2 (or As,) fluxes as well as on the substrate temperature has been investigated and can be explained qualitatively. The 'smoothing' effect of Sb during the growth has been observed.