Antioxidant compounds can be useful to prevent several degenerative diseases or as preservative in food and toiletries. Species of the Myrtaceae family are able to accumulate phenolic substances and those are closely related to the antioxidant activity due to their capacity to scavenge free radicals, protect against lipid peroxidation and quench reactive oxygen species. These facts prompted us to investigate the antioxidant capacity of the ethanolic extracts of the leaves of four Myrtaceae plants collected of the south of Brazil: Eugenia chlorophylla O. Berg., Eugenia pyriformis Cambess, Myrcia laruotteana Cambess and Myrcia obtecta (Berg) Kiacrsk. The antioxidant potential was performed using the DPPH (a single electron transfer reaction based assay) and ORAC (Oxygen Radical Absorbance Capacity, a hydrogen atom transfer reaction based assay) assays. Moreover, the total soluble phenolic content was also measured using the Folin-Ciocalteu reagent. A preliminary evaluation of the ethanolic extracts of these Myrtaceae plants revealed high levels of phenolic compounds (343.7-429.3 mg GAE) as well as high antioxidant activity according to both methods (1338 a 3785 micromol of TE/g of extract in ORAC and SC50 in the range of 1.70 and 33.7 microg/mL in the DPPH). The highest antioxidant activity obtained by DPPH assay was exhibited by ethanol extract of the leaves of E. pyriformis (1.70 microg/mL), followed by extracts of M. laruotteana (3.38 microg/mL) and M. obtecta (6.66 microg/mL). In comparison with controls, in the DPPH assay, the extract of E. pyriformis was more active than trolox (SC50 = 2.55 microg/mL), while the extracts of M. laruotteana and M. obtecta were more actives than quercetin (SC50 = 7.80 microg/mL). In the ORAC assay, all species also show good antioxidant capacity (>1000 micromol of TE/g). Initial HPLC-UV/DAD and ESI-MS confirmed the presence of phenolic acids constituents in the ethanol extracts. The results indicate the presence of compounds possessing promising antioxidant/free-radical scavenging activity in the analyzed extracts of Myrcia and Eugenia plants of the south of Brazil.