Samples of Sr2Fe2-xMoxO6 were prepared by solid-state reaction in air and 5%H-2-95%N-2. X-ray diffractometry was used to identify the phases and evaluate the lattice parameters. It is found that molybdenum ions can dissolve in the SrFeO3 even if the sample is heated in air but the solubility is limited. The solubility can be enhanced by heating the sample in low oxygen partial pressure, which is attributed to the larger ionic radii of Fe3+ and Mo5+ than that of Fe4+. The degradation of Sr2Fe2-xMoxO6 in water and air is also reported.