Medicinal plants are rarely used as antioxidants in folk medicine, but their claimed therapeutic properties could be due, in part, to their capacity for scavenging oxygen free radicals which may be involved in many diseases. The aim of this work was to compare the capacity of polar extracts (MeOH) from Byrsonima crassa, Byrsomina fagifolia, Byrsonima intermedia and Byrsonima coccolobifolia to eliminate free radicals in vitro by the DPPH photometric assay. Ethanol solution of the extract (50ul) at different concentrations, were mixed with 100ul of a (0.3mM) DPPH etanol solution. The absorbance was measured at 517 nm (ABS sample) after 30 min of reaction at 25ºC. DPPH solution plus ethanol were used as a negative control. Quercetin and trolox were used as reference antioxidant. The capability to scavenge the DPPH radical was calculated as DPPH scavenging effect (%) = [(A₀ – A₁/A₀) x 100] were A₀ is the absorbance of the negative control and A₁ is the absorbance in the presence of sample. All extracts tested were highly effective in reducing DPPH and the highest activity was observed in B. fagifolia (reduced the stable radical DPPH in about of 84%) almost the same for quercetin and trolox used as control. Based on the mechanism of reduction of the DPPH molecule, it is possible to infer, at least in part, to the presence of substances with available hydroxyl groups in extracts plants. Compounds able to donate hydrogen are derived from shikimate pathway, as for example, flavonoids.  Recently, studies have implicated the generation of oxygen derived free radicals and lipid peroxidation as one of the most important mechanisms involved in the pathogenesis of gastric ulcer. An ethnopharmacological survey carried out showed that these plants are used to treat gastric pain and gastritis. These uses may be directly linked to the content in phenolic compounds and consequently to their free radical scavenging activities. Phytochemical investigation of Byrsonima crassa afforded five known substances: quercetin-3-O-β-D-galactopyranoside, quercetin-3-O-α-L-arabinopyranoside, the biflavonoid amentoflavone, (+)-catechin and (−)-epicatechin but the others species have not its phytochemical information described yet.