Our study was carried out on leaves of Marianna rootstock (Prunus cerasifera Ehrh. × Prunus munsoniana Wight and Hedr.) cultivated in Egypt for investigation of antioxidant active metabolites. Leaves were extracted using solvents with increasing polarities (petroleum ether, methylene chloride, ethyl acetate and 80% methanol), in addition to 70% ethanol (the crude extract ). Preliminary phytochemical screening revealed presence of sterols and/or triterpenes, carbohydrates and/or glycosides, flavonoids, phenolic acids, saponins and tannins, whereas coumarins and alkaloids were absent. Total phenolic acids and total flavonoids contents were amounted to 46.18 mg gallic acid equivalent (GAE/g) and 44.38 mg catechin equivalent (CE/g), respectively. HPLC analysis of polyphenols revealed 8 compounds identified in crude extract ; kaempferol (0.4483 mg/g) was the major flavonoid followed by catechin, quercetin and rutin. Whereas caffeic acid (26.67542 mg/g) was the major phenolic acid followed by chlorogenic acid. Chromatographic investigation of methanol fraction successive extract yielded isolation and spectroscopic identification of 4 flavonoids; kaempferol -3, 7-O-α-L- di-rhamnoside, kaempferol -7-O- α-L- rhamnoside, kaempferol 3, 7-O-β-D-di-glucoside and quercetin-7-O-β-D- glucoside,4'-O-α-L- rhamnoside. In-vitro antioxidant properties of leaves different extractives were evaluated using different assays; DPPH, nitric oxide, metal chelating ability and total antioxidant capacity that showed promising antioxidant efficacy of plant extracts compared with L-ascorbic acid and BHT standards.