Garnet-based ceramics doped with Gd, Th, and Ce as waste surrogates and compositions: (Ca1.5GdTh0.5)ZrFeFe3O12 (G3) and Ca2.5Ce0.5Zr2Fe3O12 (G21) were prepared at 1300 °C in air. Corrosion rates in deionized water measured using an MCC-2 procedure were found to be (in g × m-2 × day-1): 10-6 for Ce (G21), 3×10-5 for Gd and 10-6 for Th (G3). Corrosion rates of Ce, Gd, and Th in an acid solution (0.01 M HCl) were 2 × 10-1 (G21), 4 × 10-3 and 10-3 (G3), respectively. Chemical durability of the garnet ceramics is comparable to durability of titanate zirconolite and pyrochlore samples under similar conditions. Scanning electron microscopy has revealed no alteration of the sample surfaces after their contact with water, and the presence of newly formed iron-enriched phases of 1 to 3 micrometers in size, after interaction of the G21 sample with acid solution for 30 days. High leaching of the elements from the Ce-loaded garnet may be due to reduction of Ce in acid solution to Ce(III) or may be explained by lower stability of the structure of garnets (Ca2.5An0.5)Zr2Fe3O12 compared to (Ca1.5GdAn0.5)(ZrFe)Fe3O12, An = Ce4+ and Th4+. It was found that the (Ca2.5Ce0.5)Zr2Fe3O12 and (Ca2.5Th0.5)Zr2Fe3O12 garnets have distorted the elementary unit cell with decreasing lattice symmetry to tetragonal.