A novel compound, a rare earth complex oxide SnEr2O4 was synthesized by the thermal decomposition of its oxalate precursor prepared by Rheological Phase Reaction Method. TG, IR, XRD and XPS were used to prove the formation of the compound SnEr2O4. The structure of SnEr2O4 was defined by Rietveld analysis. SnEr2O4 is cubic, Pm3m, a = 7.3735 Angstrom, V = 400.88 Angstrom(3), Z = 4, D-x = 8.573 g/cm(3), D-m = 8.2 g/cm(3).