Abstract: The Y-doped hexagonal perovskites ErMnO3 were synthesized and systematically investigated by Xray diffraction, magnetometry and neutron powder diffraction, to elaborate the effect of the magnetic rareearth ions on the magnetic Mn3+ sublattice as well as the magnetization property at low temperature. The results of both Xray and neutron diffraction show that the crystal structure and magnetic structure are almost unaffected by Y3+ doping and maintain the undoped structure, implying a weak interaction between Er3+ and Mn3+. Meanwhile, an anisotropic thermal expansion behavior is disclosed for this hexagonal system, with a dilates while c contracts with the increase of temperature. The neutron diffraction data confirm that the ordering temperature is approximately 79 K for Er0.4Y0.6MnO3 sample below which Mn3+ sublattice order adopts a Γ2(P63c′m′) or Γ4(P63′c′m) ground state, identical to Er0.8Y0.2MnO3. The magnetometry measurements show that the spin of Er3+ is ordered and coupled with Mn3+ sublattice at low temperature, and the magnetization is weakened by the Y3+ doping. In conclusion, the result provides a deep insight into the magnetism of hexagonal ErMnO3 system, which offers a guidance for the potential application of this intriguing system.