The effect of betel nut chewing lead to oral disease is well-known, but it leading to nephropathy is rarely discussed. Betel nut itself and its additives, such as unriped fruit of piper linn and slaked lime, lead to impairment of the renal function. Any subjects ingesting a large amount of Ca (OH) or CaCO from the slaked lime will develop milk-alkali syndrome. Arcoline of the betel nut, its chemical derivatives and the safrole of the unriped fruit of piper linn will lead to renal cell DNA break-up and kidney. We will focus on the hazard of betel nut chewing which causes the damage of the kidneys in this paper.