Xanthium strumarium L. is a medicinally important plant which is widely used in traditional healthcare system for treatment of various ailments like infections, inflammation and respiratory disorders. The present study was planned to evaluate the phytochemical composition and antioxidant potential of different parts of the plant i.e. roots, stems, leaves and flowers using aqueous, methanolic and petroleum ether extracts. The extractive values showed significant variation depending on the plant part and solvent used. Methanolic extracts showed maximum extraction efficiency especially from stem (384 mg/g dry weight) and leaf (352 mg/g dry weight). Preliminary phytochemical screening revealed the presence of wide range of primary and secondary metabolites such as carbohydrates, proteins, tannins, alkaloids, flavonoids, phytosterols, saponins and terpenoids. Methanol was found to be the best solvent for extraction. Quantitative analysis revealed organ-specific differences in the distribution of metabolites. Leaves had highest concentrations of starch (21.82 ± 1.18 mg/g dw), total soluble sugars (16.88 ± 0.38 mg/g dw), ascorbic acid (1.23 ± 0.16 mg/g dw), chlorophyll (3.11 ± 0.08 mg/g dw), carotenoids (1.92 ± 0.11 mg/g dw), phenols (1.11 ± 0.11 mg/g GAE) and phytosterols (2.27 ± 0.11 mg/g dw), whereas flowers had highest protein content (20.91 ± 0.72 mg/g dw). The antioxidant activity determined by DPPH free radical scavenging assay showed a concentration dependent increase in all the extracts. Among the tested samples, leaf and flower extracts showed the highest antioxidant potential with maximum scavenging activity of aqueous leaf extract (28.74%) and methanolic flower extract (28.25%) at 250µg/mL. These results suggest that Xanthium strumarium is a rich source of bioactive phytochemicals and has a significant antioxidant potential mainly in foliar and floral tissues. These results are in favour of the traditional medicinal use of the plant and also provide evidence for its potential application in pharmaceutical, nutraceutical and natural antioxidant fields.