Quercetin is an important dietary flavonoid. It`s found hugely in onion, apples, broccoli, berries, olive oil, citrus fruits, parsley, buckwheat, grapes, beans, and leafy green vegetables. It has a very potent anti-oxidant activity equals about four times more than that of vitamin E. Quercetin was well documented as anticancer, anti-hypercholesterolemia, anti-ulcer, anti-inflammatory, anti-histaminic, and anti- aging compound. We proved these effects of Quercetin by experiments which were documented in the text in addition to it`s effect as fertility and immunity booster, and anti-anemic. As Quercetin proved its ability to ameliorate all these parameters of health especially after poisoning with the very toxic compound o-anisidine, we recommend the use of Quercetin in form of medicine to treat or prevent the mentioned above diseases and by ingesting foods that contain Quercetin.