Myrcia is one of the largest genera of the economically important family Myrtaceae. Some of the species are used in folk medicine, such as a group known as pedra-hume-caa or pedra-ume-caa or insulina vegetal (insulin plant) that it is used for the treatment of diabetes. The species are an important source of essential oils, and most of the chemical studies on Myrcia describe the chemical composition of the essential oils, in which mono- and sesquiterpenes are predominant. The non-volatile compounds isolated from Myrcia are usually flavonoids, tannins, acetophenone derivatives and triterpenes. Anti-inflammatory, antinociceptive, antioxidant, antimicrobial activities have been described to Myrcia essential oils, while hypoglycemic, anti-hemorrhagic and antioxidant activities were attributed to the extracts. Flavonoid glucosides and acetophenone derivatives showed aldose reductase and -glucosidase inhibition, and could explain the traditional use of Myrcia species to treat diabetes. Antimicrobial and anti-inflammatory are some of the activities observed for other isolated compounds from Myrcia.