Fatty acids of Euterpe oleracea Mart seeds were analyzed in hexane and diethyl ether extracts. The hexane extract contained dodecanoic acid (3), tetradecanoic acid (4), hexadecanoic acid (7), and 9-octadecenoic acid (10). The diethyl ether extract contained (10). The oil of Mart seeds was obtained firstly by methanol extract and further extracted with diethyl ether. The hexane and diethyl ether extracts were then analyzed for antioxidant effects. Both extracts demonstrated a 1,1-diphenyl-2-picrylhydrazyl radical elimination effect similar to that of α-tocopherol and an active oxygen inhibition effect. Significant quantities (0.6212 mg/mL) of polyphenol, in comparison to the standard rejected gallic acid, were found in the extract oil of Mart seeds by the methanol extraction.