Flavonoids are biologically active phytochemicals that are naturally found in the everyday diet. They are bio-active polyphenolic compounds that have profound effects in inhibiting the growth and development of tumors. They are found to exert anti-tumor effects by acting in several ways: they modulate ROS production, regulate cancer cell proliferation, induce apoptosis, suppress the expression of pro-inflammatory cytokines with simultaneous increase in the expression of anti-inflammatory cytokines, and inhibit proto-oncogenes. Moreover, flavonoids eliminate the deleterious side effects of anti-cancer chemotherapeutic regimen. Thus, flavonoids can be used as a potential anti-cancer natural compound that not only achieves anti-cancer efficacy but also improves the survival and life expectancy of cancer patients.