Abstract We studied polycrystalline Ho 0.2Ca 0.8MnO 3 by neutron and X-ray diffraction. At room temperature Ho 0.2Ca 0.8MnO 3 crystallizes in a distorted orthorhombic perovskite-like structure. At T C =160(1) K we observed a structural phase transition from space group Pnma to P2 1/m. Below T N =146(1)K neutron diffractograms show sharp magnetic peaks which are due to a long-range antiferromagnetic order of the magnetic moments of the Mn-ions. We describe this magnetic order in a magnetic unit cell with lattice vectors: a mag = a chem , b mag = b chem , c mag = a chem + c chem , magnetic spacegroup P 2a(mag) 2 1 /m. The magnetic moments of the Mn-ions are alligned in (2 a mag − c mag ) -direction. The size of the ordered moment is proportional to the monoclinic lattice distortion.