Neutron diffraction techniques have been used to study the magnetic structure of DyNi 2 B 2 C. The measurements, performed on single crystals of this compound depleted in the neutron absorbing B 1 0 nuclei, show that below approximately 10K the compound is a simple collinear antiferromagnet. The moments are aligned ferromagnetically in each rare-earth carbon layer perpendicular to the c-axis with the magnetic moments of two consecutive layers aligned in opposite directions. In contrast to the case of both HoNi 2 B 2 C and ErNi 2 B 2 C no modulation along thea * direction was observed in this compound.