The static antiferromagnetic order as well as the magnetic excitations in doped iron-based superconductors display a remarkable anisotropy, which is inherited from their corresponding undoped parent compounds. For BaFe2As2 the single-ion anisotropy was determined by polarized inelastic neutron scattering revealing the astonishing fact that it is easier to rotate the spin out of the FeAs-layers than within. Due to the great relevance of magnetic anisotropy in Fe-based superconductors and due to the persisting controversy about the origin of longitudinal excitations we consider it important to study the magnetic anisotropy in a second undoped compound, SrFe2As2, for which unpolarised neutron scattering found significant differences.