[en] The magnetic properties (magnetization, coercivity and exchange interactions) of Dy₃Co₁₁B and Er₃Co₁₁B compounds have been studied. The saturation moments at 4.2 K are 19.1 and 14.2μ_B/f.u. for Dy₃Co₁₁B₄ and Er₃Co₁₁B₄, respectively. The temperature dependence of the coercivity (H_c) for the Er₃Co₁₁B₄ compound is nearly linear when the logarithm of H_c is plotted versus T. This linear dependence has been explained by a thermally activated process of domain wall motion. The molecular field approximation was applied to calculate the intersublattice exchange interactions considering the experimental Curie temperature of the investigated compounds. ((orig.))