DC. (Myrtaceae), popularly known as "cereja-do-Rio-Grande", is a native tree from Brazil, popularly used as a hypoglycemiant. Crude hydroalcoholic extract (CHE) and fractions (insoluble (FI), dichloromethane (FDM), ethyl acetate (FEA) and butanol (FBu)) of leaves were assessed to determine the phenolic chemical composition by HPLC-ESI-MS/MS. 10 compounds were identified, being 7 new for this species: rutin, isoquercitrin, luteolin-7- -rutinoside, mandelic acid, naringenin, luteolin-7- -glucoside and salicylic acid. Extract and fractions showed inhibitory activity on acetylcholinesterase (AchE) enzyme (best result: IC = 44.19 µg mL , for FEA) and α-glucosidase (α-Glu) (best result: IC = 31.25 ± 0.15 µg mL , for CHE). The observed antioxidant and inhibitory activity on the AchE and α-Glu is due to, at least in part, the presence of phenolic compounds in the samples.