BaCo(Al, Ga)(11)O-19 with beta-alumina structure was found to be an effective catalyst for NOx reduction and successfully synthesized by the coprecipitation method using metal nitrates and ammonium carbonate. Anisotropic BaCo(Al, Ga)(11)O-19 particles crystallized at 1100 degreesC for 2 h through the coprecipitation method. BaCo(Al, Ga)(11)O-19 supported on a cordierite honeycomb had the NOx removal activity with methane over 500 degreesC in the presence of excess oxygen.