A detailed study of the magnetic properties of the tetragonal rare earth compound DyRu2Si2 is presented. Magnetization measurements on a single crystal as well as specific heat and resistivity measurements on a polycrystal show features which are typical of a long-period commensurate system in the presence of a huge uniaxial anisotropy. Multistep metamagnetism occurs below the Neel temperature TN=29 K, in particular at low temperatures. In the low-field low-temperature region, a new magnetic phase has been discovered with an anomalous behaviour.