We report on the low-temperature magnetic properties of the perovskite, which were characterized by means of single crystal and powder neutron scattering, and by magnetization measurements. Below  K, moments form an antiferromagnetic structure with an easy axis of magnetization lying in the plane. The magnetic moments are inclined at an angle of to the axis. We show that the ground-state Kramers doublet of is made up of primarily eigenvectors and well separated by a crystal field from the first excited state at meV. This leads to an extreme Ising single-ion anisotropy, . The transverse magnetic fluctuations, which are proportional to , are suppressed, and only moment fluctuations along the local Ising direction are allowed. We also found that the Dy-Dy dipolar interactions along the crystallographic axis are two to four times larger than in-plane interactions.