Few studies were performed with wild plants, and researches are important to plants valorization and conservation. In this work we evaluated the nutritional composition, bioactive compounds and antioxidant activity of an unconventional food plant, mostly considered as a weed (Rumex obtusifolius). All the analyses were performed in leaf and root: moisture, ashes, lipids, proteins, carbohydrates, pH and total acidity. Phenolic, flavonoids, flavonols, antioxidant activity (DPPH, ABTS and FRAP) were quantified in aqueous, ethanolic and hydroethanolic extracts. Results show that hydroethanolic extract from root presented more bioactive compounds (p<0.05) and more antioxidant activity by ABTS and FRAP assay; ethanolic and hydroethanolic extract from root presented non-significant difference (p>0.05) by DPPH assay. Pearson’s correlation coefficients proved that antioxidant capacity is related to the presence of bioactive compounds in the root and leaf of Rumex obtusifolius. Using principal component analysis the extracts were classified in tree groups according to extraction potential, been the root hydroethanolic and ethanolic extracts the highest. This unconventional spread worldwide plant presents a great content of nutritional composition and has the potential to be used in human consumption, providing nutrients and bioactive compounds with high antioxidant activity.