Technical Abstract: Rosmarinic acid (RA) is an important polyphenol that is found in a variety of herbs including Ocimum canum sims (locally called eme or akokobesa in Ghana). Aqueous extracts from the leaves of O.canum are used as an antidiabetic herbal medicine in Ghana. Interestingly, rosmarinic acid content and polyphenol profile in the aqueous extract of this herb found in Ghana and widely for medicinal purposes has not being determined. Analytical TLC was used to examine the composition of the polyphenols in leaf extracts. The total polyphenol content in the leaf aqueous and methanol extracts, as determined by Folin - Ciocalteu reagent method, were 314 mg of gallic acid equivalent/gram of leaf sample and 315 mg of gallic acid equivalent/gram of leaf sample respectively. The total flavonoid concentration as determined by the aluminum (III) chloride method was 135 mg of catechin equivalent/gram of leaf sample. High performance liquid chromatography (HPLC) coupled to an electrospray Q-TOF mass spectrometer (ESI-Q-TOF MS) was also used to determine the polyphenol fingerprint profile in the leaf extracts of O. canum. The average rosmarinic acid concentration in the O. canum leaf extracts was 1.69 mg/g dry weight. The polyphenolic content in the leaf extract of O.canum sims was attributed predominantly to rosmarinic acid and caffeic acid derivatives. The polyphenol finger print obtained in this analysis could be used as reference standard for neutraceutical analysis from this herb.