The present study was aimed to evaluate the in vivo radioprotective efficacy of quercetin-3-O-rutinoside (PMC-1), the key bioactive constituent flavonoid glycoside isolated from the whole plant of Pilea microphylla was evaluated. In vivo survival studies established the optimum effective dose of PMC-1 at 25 mg/kg/i.p. At the optimum dose, PMC-1 prevented the depletion of endogenous antioxidants in the liver of irradiated mice. In vivo protection towards gastrointestinal tract and haematopoietic system was confirmed by the restoration of radiation-induced reduction in villi height, number of crypt cells and spleen index. PMC-1 also attenuated the radiation-induced apoptosis in spleenocytes significantly. Single cell gel electrophoresis of peripheral blood leukocytes showed inhibition of radiationinduced DNA damage by PMC-1. PMC-1 pretreatment significantly reversed the changes by increasing pro-survival (ERK) and decreasing pro-apoptotic (BAX) gene expressions compared to radiation control. Thus, PMC-1 exhibits protective effects against γ-radiation and the probable mechanism of action involves maintenance of antioxidant enzymes, prophylactic action and inhibition of apoptosis.