From ancient times Pleurotus ostreatus is a popular edible mushroom for its test, flavor, texture and gastronomic delicacy. In addition, recent literature reports have revealed diverse therapeutic importance of this mushroom. However quality standard of this species is still unexplored. Therefore the present study aims at investigating the microscopic, physical and fluorescent characters of dry powder derived from basidiocarp with the objective to establish pharmacognostic standard of this popular oyster mushroom. Furthermore, a methanolic fraction was prepared from the macrofungus and preliminary mycochemical screening revealed presence of phenols, flavonoids, ascorbic acid, β-carotene and lycopene. For chromatographic study, HPLC was performed to achieve a phenolic fingerprint which indicated existence of 13 components. DPPH and total antioxidant assays were executed to determine the antioxidant potential of this methanolic fraction. Result demonstrated high efficiency of the mushroom as radical scavenger indicating potentiality to be used as a therapeutic drug. The aforementioned data presented in this work are valuable to assist identification of crude drugs prepared from P. ostreatus.