Eugenia uniflora L. (Myrtaceae) is a plant species used in folk medicine for treatment of various disorders. This study aims to quantify the phenolic and flavonoid contents of E. uniflora aqueous methanolic extract (AME), identification of its major constituents, as well as the evaluation of its biological activity. Quantification was performed using colorimetric assays. Column chromatographic separation was used for isolation of the major phenolic constituents while their structures were elucidated by 1D- and 2D Nuclear magnetic resonance spectroscopy (NMR) spectra. Alkaloids were identified using gas chromatography-mass spectrometry (GC-MS) analysis. The antidepressant activity of E. uniflora AME in mice was evaluated using the tail suspension test (TST). The weight control effect was evaluated by serial weighing. The results showed high phenolic and flavonoid contents of E. uniflora AME. The chromatographic investigation identified a new flavonoid, myricetin 3-O-(4'', 6''-digalloyl) glucopyranoside, for first time in this genus, along with four flavonoids and phenolic acids. Integerrimine alkaloid was identified through GC/MS analysis. Administration of E. uniflora AME significantly reduced the immobility time in mice (P value of < 0.0001) in a dose- dependent manner for doses of 1, 10, 50 and 100 mg/kg. Also, a non-significant weight reduction in mice chronically treated with the E. uniflora AME was observed. Our study reports the isolation of myricetin 3-O- (4'', 6''-digalloyl) glucopyranoside from E. uniflora. It confirms that E. uniflora leaf extract has an antidepressant and anti-obesity effect. Key words: Eugenia uniflora, flavonoid, alkaloid, depression, obesity.