The aleurone layer of Oryza sativa cv. Heugjinmi yielded a new quinolone alkaloid, 4-carbomethoxy-6-hydroxy-2-quinolone (1), showing moderate antioxidative activity in a 1,1-diphenyl-2-picrylhydrazyl free-radical scavenging assay. Physical and spectroscopic evidence has determined the structure of the compound.