A qualitative characterization of the main phenolic compounds from ethanol extract of Hymenaea martiana was carried out by high performance liquid chromatography with diode array detection (HPLC-DAD). The total phenolics content of the plant extracts was determined by the Folin-Ciocalteu method. Total flavonoid content also was measured. Antioxidant activities of the extracts were evaluated by using DPPH radical scavenging and β- carotene-linoleic acid bleaching and compared with ascorbic acid, BHA and BHT used as reference compounds. The total phenolic content was of 428.50 ± 5.91 and 705.50 ± 7.22 mg of gallic acid equivalent/g for EtOH and AcOEt extracts, respectively. The total flavonoids content was of 394.90 ± 8.43 and 479.60 ± 10.38 for two extracts, respectively. All extracts exhibited good antioxidant activities. The EtOH extract showed better antioxidant activity than ascorbic acid and BHA using by DPPH method, with a value of IC50 of 0.84 ± 0.26 μg/ml. BHT was the most effective antioxidant. The results obtained show that phenolic compounds contribute to the antioxidant activity of the extract. Further studies will be conducted to isolate the chemical constituents responsible for antioxidant activity.