The support materials of ruthenium-based catalysts for ammonia synthesis were preparedusing mixed solutions composed of magnesium nitrate, aluminum nitrate and calcium nitrate with acertain ratio. The catalysts supported on complex oxides were more active and the optimal activitytemperatures were lower than that supported on single oxide under the same conditions. Thecatalyst with Mg-Al complex oxide as support prepared by calcinating hydrotalcite-like compoundhad significantly higher activity, 38.42 mL NH3?h-1?g-1 at 673 K. The BET determination showedthat the Mg-Al complex oxide possessed large surface area, 140.95 m2?g-1, similar to γ-Al2O3.