The qualitative and quantitative compositions of chinotto juice in two different maturation periods were determined via chromatographic separation of extracted aliquots of juice of Citrus x myrtifolia Raf. by using reverse-phase LC-DAD-ESI-MS-MS. This provides a comprehensive chromatographic evaluation of 11 compounds (furanocoumarins and flavonoids C- and O-glycosides). Five flavonoids and two furanocoumarins were identified for the first time in chinotto juice: two C-glucosides (vicenin-2 and lucenin-2 4'-methyl ether), two O-glycosides (narirutin and rhoifolin), and a 3-hydroxy-3-methylglutaryl flavanone (brutieridin). Bergapten and epoxybergamottin were the primary furanocoumarins found. Overall, the juice from immature chinotto fruits is richer in bioactive compounds than that obtained from ripe fruits. The free radical and superoxide anion scavenging activities of juice from both green and ripe fruits were assessed, and results showed that the former is much more efficient in scavenging radical and superoxide species than the latter.