We succeeded in purifying the carotenoid produced by Bacillus firmus GB1 using chromatography on polystyrenic synthetic adsorbents, and identified it as 4,4'-diapolycopene-4,4'-dioic acid by HRESI-MS and NMR analyses of it and its dimethylester. In addition, we clarified the singlet oxygen (¹O₂) quenching activities of 4,4'-diapolycopene-4,4'-dioic acid and its methyl esters (mono and dimethyl ester). Their IC₅₀ values were 5.8 μM, 6.0 μM, and 6.2 μM, respectively. To our knowledge, this is the first report concerning the isolation and antioxidative activity of 4,4'-diapolycopene-4,4'-dioic acid, a product of the C30 carotenoid biosynthesis pathway.