Abstract We present detailed do magnetization and magnetic resonance for an Eu 1.9Y 0.1CuO 4 single crystal. The substitution of Eu by non-magnetic Y 3+ allowed us to measure the weak ferromagnetic properties of the ordered Cu lattice with the interference of just the weakly magnetic Eu 3+ ions. A Néel temperature, T N ∼ 250 K, and a value of the saturation magnetization m s (6 K) ∼ 5 × 10 −3 μ B/Cu-atom, were obtained from the data. We observed anisotropy effects in the magnetization within the CuO 2 planes. The data were analyzed using a four sublattice magnetic free energy for the ordered Cu spins. From the magnetic resonance data taken at Q band (34 GHz) we have determined the temperature dependence of the out-of-plane and in-plane anisotropy fields. Using an average value for the exchange field 〈 H e〉 = 80 G, we estimate a value for the interplanar exchange constant, Jτ = 19 mK, similar to the values previously found in La 2CuO 4 and Y 2CuO 4.