In order to investigate chemical scavenging mechanism of singlet oxygen, superoxide anion radical, and hydroxyl radical by carotenoids, reaction products obtained by reacting β-carotene or zeaxanthin with singlet oxygen, superoxide anion radical, and hydroxyl radical were analyzed by LC/PDA ESI-MS, and ESR spectrometry. β-Carotene endoperoxides were identified as the major reaction products of β-carotene and singlet oxygen, while β-carotene epoxides were the major reaction products of β-carotene and superoxide anion or hydroxyl radical. Similar results to those for β-carotene were obtained with zeaxanthin.