Abstract: The crude extract and 4 fractions of aerial parts of cultivated motherwort (Leonurus cardiaca L.) were investigated for their total phenolic and flavonoid contents and antioxidant activities. The phenolic and flavonoid contents were determined using Folin-Ciocalteu assay and proposed assay of pharmacopeia where as antioxidant activity of samples were measured by 2 tests: DPPH and FRAP assays. Buthanolic fraction showed the highest antioxidant activity with the FRAP value of 1.735±0.07 μmol g-1 and DPPH inhibitory percentage of 57.76% μg mL-1 as well as the greatest phenolics content (48.37±3.76 mg of gallic acid equivalents g-1). The highest total flavonoid content was revealed in methanolic-aqueous fraction (50.21± 0.65 mg of hyperoside equivalents g-1). There was a direct correlation between total phenol and antioxidant activities which could introduce phenols as the main antioxidants of L. cardiaca L. extracts.