The composition and antioxidant properties of a methanol: acetic acid (99:1, v/v) soluble crude extract isolated from S. officinalis L. leaves through maceration and selected fractions isolated thereof are presented in this study. The total phenol content was estimated as gallic acid equivalents, whilst qualitative-quantitative phenolic content was determined using high performance liquid chromatography with photodiode array detection. Antioxidant evaluation consisted of ferric reductive capacity and 1,1-diphenyl-2-picrylhydrazyl and hydroxyl free radical scavenging determinations. The crude extract contained hydroxybenzoic acids, hydroxycinnamic acids, flavonoids and diterpenoids, whilst caffeic acid, carnosic acid, luteolin, luteolin-7-O-glucoside and rosmarinic acid were identified from their chromatographic and spectral characteristics and quantified from their respective calibration curves. The crude extract and sub-fractions demonstrated varying degrees of efficacy in the antioxidant-related assays used, except the n-hexane fraction, which was unable to reduce iron(III) at reasonable concentrations. Although the positive controls, ascorbic acid, BHA and BHT, were more potent than the S. officinalis samples, two fractions were significantly (p < 0.05) more potent iron(III) reducing agents than pycnogenol, a proanthocyanidin-rich commercial preparation.