The qualitative and quantitative phytochemical composition and antioxidant activity of the leaves and stem bark of Annona muricata (soursop) were investigated. Plant samples were collected from Otuoke community, Ogbia Local Government Area, Bayelsa State, Nigeria. The collected plant parts were chopped, dried, and extracted using absolute ethanol, followed by concentration under vacuum. Both the leaf extract (IDL) and stem extract (IDS) were analyzed for their phytochemical constituents using standard procedures. The analysis revealed the presence of several phytochemicals including alkaloids, phenols, flavonoids, glycosides, tannins, saponins, and terpenoids. The leaf extract contained alkaloids (13.0 mg), phenols (0.440 mg), flavonoids (8.3 × 10^-5 mg), cardiac glycosides (486.0 mg), tannins (10.6 mg), and terpenoids (322.0 mg), while the stem extract had alkaloids (20.0 mg), phenols (0.70 mg), flavonoids (8.2 × 10^-5 mg), cyanogenic glycosides (300.0 mg), tannins (6.2 mg), and terpenoids (215.0 mg). Statistical analysis using the t-test showed no significant difference in the concentrations of these phytochemicals between the leaf and stem extracts at p < 0.05. The antioxidant activity of both extracts was evaluated using the 1,1-diphenylpicrylhydrazine (DPPH) method, with both extracts showing significant antioxidant potential across a dose gradient range of 1.0 mg/ml to 0.625 mg/ml. This study confirms that both the leaves and stem bark of Annona muricata are rich in phytochemicals and exhibit noteworthy antioxidant activity, thereby validating the traditional ethnomedicinal uses of the plant