The effects of Y-doping on the phase formation in an FeSO 4 Na 2 CO 3 suspension system were determined. The phase, microstructure and thermal stability of the samples were studied by XRD, TEM and TG-DTA. It was found that Y appears to restrain the nucleation and growth of α-FeOOH, but facilitates the formation of γ-FeOOH. Partly due to Y-doping, tetragonal γ-Fe 2 O 3 from direct dehydration of γ-FeOOH has high thermal stability, and the phase transition temperature of γ-Fe 2 O 3 →α-Fe 2 O 3 is increased to 725 °C. The properties of cubic γ-Fe 2 O 3 obtained from Y-doped α-FeOOH were also investigated.