Guava (Psidium guajava) is a botanical plant that has been used for a long time as a ceremonial and / or medicinal plant. However, chemical and biological activity of this plant is hidden and very few reported studies used an analytical method, purification and analysis techniques to characterize the components of this medicinal plant. This plant has the potential to function as a therapeutic agent that can protect our body from disorders such as cancer and chronic heart disease among others. It is highly recognized that fruits, vegetables, tea and many natural products are rich in polyphenolic compounds with nutraceutical, antioxidants and antimicrobials benefits. For this reason the objectives of this study were to: 1) identify and quantify the presence quercetin, rutin, gallic acid and ellagic acid in mature lyophilized guava (Psidium guajava) leaves using LC-MS (Liquid Chromatography-Mass Spectrometry) analysis, 2) quantity the total phenols using Folin Ciocalteu spectrophotometric methodology and 3) measure the antioxidant activity of the extracts tested with ORAC (Oxygen Radical Absorbance Capacity) methodology. LC-MS analysis identified the following compounds in the analyzed fourteen clones: galic acid, ellagic acid, quercetin. The average concentration of the compounds identified was: 0.07±0.02mg/g gallic acid, 3.76±0.12 mg/g ellagic acid and quercetin 0.25±0.08mg/g. Rutin was not identified in any of the analyzed clones. The average total amount of phenols found for the fourteen clones tested was 107.6±5.3mg/g GAE (Gallic Acid Equivalent) for the methanolic phase and 2.6±0.3mg/g GAE for aqueous phase. The average antioxidant activity found for the fourteen clones of guava was 0.73 ± 0.10μmolTE (Trolox Equivalent) / g in the aqueous phase and 38.01 ± 15.23μmolTE methanolic phase.