Extracts of mulberry fruits (Mores sp.) were prepared from 8 cultivars harvested at 4 stages of maturity, and their radical-scavenging activity, anthocyanin content, and total phenolic content were measured. The radical-scavenging activity was evaluated by a spectrophotometric assay using the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH center dot) in a 96-well microplate. Mulberry fruit extracts exhibited the DPPH center dot-scavenging activities, ranging from 2.5 to 20.3 mu mol-Trolox equiv/g-FW Their activities were variable during maturation, and the highest activity was observed in the fully mature mulberry fruit in all cultivars. Anthocyanin was scarcely present in the immature mulberry fruits; however, its content increased as the fruit matured in all cultivars. On the other hand, all immature mulberry fruits contained non-anthocyanin phenolic compound. An on-line high-performance liquid chromatography (HPLC) method for the detection of DPPH center dot-scavenging compounds revealed the difference in predominant radical scavengers between the immature and fully mature stages in the Miran 5 cultivar. Four major radical scavengers in the Miran 5 cultivar were assigned to 2 caffeoylquinic acids (chlorogenic acid and its isomer) and 2 anthocyanins (cyanidin 3-glucoside and cyanidin 3-rutinoside) in the immature and fully mature stages, respectively, by LC-ESI-MS/MS analysis. The change in the content of 4 compounds in mulberry fruits during maturation demonstrated that the most likely contributors to the DPPH center dot-scavenging activity were caffeoylquinic acids in the immature mulberry and anthocyanins in the mature and fully mature mulberry.