Containerless levitation technique, where the undercooling can be treated as one of the major thermodynamic parameters, was used to study the influence of oxygen partial pressure (inline image) on the microstructure and physical properties of rare-earth orthoferrites RFeO3 (where R = Rare-earth element) in the inline image ranges from 105 to 10−1 Pa. The microstructure of the as-solidified samples changed into orthorhombic RFeO3 (o-RFeO3), metastable hexagonal RFeO3 (h-RFeO3), and Fe2+-containing RFe2O4 and a new metastable R3Fe2O7 phases with decreasing inline image. The effect of inline image on the magnetic properties was indicated as that the saturation magnetization gradually increased for R = La to Yb and decreased for R = Lu with decreasing inline image due to the formation of metastable and magnetic phases such as Fe3O4 and Fe.