Ground beef with 10%, 15%, or 20% fat were added with none, 0.05% ascorbic acid + 0.01%alpha-tocopherol, or 0.05% ascorbic acid + 0.01%alpha-tocopherol + 0.01% sesamol, and irradiated at 0 or 2.5 kGy. The meat samples were displayed under fluorescent light for 14 d at 4 degrees C. Color, lipid oxidation, volatiles, oxidation-reduction potential (ORP), and carbon monoxide (CO) production were determined during storage. Irradiation increased lipid oxidation and total volatiles of ground beef regardless of fat contents. Ascorbic acid + alpha-tocopherol + sesamol treatment was the most effective in reducing lipid oxidation during storage. The production of ethanol in nonirradiated ground beef increased dramatically after 7 d of storage due to microbial growth. Total aldehydes and hexanal increased drastically in irradiated control over the storage period, but hexanal increased the most by irradiation. L*-values was decreased by irradiation, but increased in all meat regardless of fat contents as storage period increased. Irradiation reduced the redness, but fat contents had no effect on the a*-value of ground beef. Sesamol lowered, but ascorbic acid + alpha-tocopherol maintained the redness of irradiated beef up to 2 wk of storage. The yellowness of meat was significantly decreased by irradiation. The reducing power of ascorbic acid + alpha-tocopherol lasted for 3 d, after which ORP values increased. Irradiation increased CO production regardless of fat content in ground beef. In conclusion, up to 20% fat had no effect on the quality change of irradiated ground beef if ascorbic acid + alpha-tocopherol was added.