In this article, Gd3−xErxFe5O12 powders with x= 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 were prepared by solid-state reaction method. The properties of the prepared samples were examined by X-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometry, and differential scanning calorimetry. The XRD patterns of the powders show a single-phase structure and were found to agree with the standard pattern of rare earth iron garnet. Room temperature Mössbauer spectra of the powders indicate that iron is present in three magnetic sites corresponding to two octahedral sites and one tetrahedral site. The saturation magnetization increased with increasing erbium substitution, and the Curie temperature decreased slightly.