Parkinsonia aculeata L. is a species native to the Brazilian Caatinga and is used in folk medicine as an antihyperglycemic, antimalarial and amebicidal agent. This work evaluated the antioxidant and polyphenol content of Parkinsonia aculeata leaf extracts cultivated in the Brazilian Caatinga. P. aculeata aqueous and methanolic leaf extracts were investigated for their antioxidant capacities by four in vitro methods: DPPH radical scavenging, hydrogen peroxide scavenging, phosphomolybdenum and reducing power assays. The total polyphenol content was measured by the Folin-Ciocalteu method. Both extracts showed high activity, while the methanolic extract had the best results in all antioxidant systems (p < 0.001). These results can be explained by higher polyphenol content found in this extract. Our results showed that P. aculeata extracts displayed potent antioxidant and radical scavenging properties, supporting the ethnomedical use of this plant for treatment of diseases.