Quercetin (3,5,7,3',4'-pentahydroxy flavone) is the extensive class of polyphenolic flavonoids ubiquitously found in plants such as apples, onions, seeds, tea, berries etc. It has diverse biological activities including anti-proliferative, apoptotic, prevents oxidant injury and cell death by several mechanisms which includes scavenging oxygen radicals, protecting against lipid peroxidation and chelating metal ions. Our studies proved that quercetin induces cell cycle arrest and regulates uPA and uPAR mRNA expression in prostate cancer cells. Quercetin reverses the EGF induced epithelial mesenchymal transition, migration and invasion in prostate cancer. Apart from antioxidant property, quercetin acts as a neuroprotectant through restoration of Purkinje cells of cerebellum and pyramidal cells of cerebral cortex of PCB treated adult male rats. Behavioral analysis claims drastic revitalization of cognitive function like learning and memory on treatment with quercetin. Thus quercetin prevents prostate cancer metastasis in prostate and breast cancer cells. It also prevents the degeneration in the brain regions in PCB treated rats. Depend on the nature of the cell quercetin acts as friend and foe.