Hypomagnesemia is one of the well-known side effects in patients receiving cisplatin-containing chemotherapy. However, the relevance between hypomagnesemia and cisplatin-induced nephrotoxicity remain to be completely elucidated. Although patients with esophageal and hypopharyngeal cancer are susceptible to dehydration, there is no evidence yet that magnesium supplementation for these patients will prevent nephrotoxicity during cisplatin-containing chemotherapy. The aim of this study was to examine the effect of magnesium supplementation on the prevention of cisplatin-induced nephrotoxicity for patients with esophageal and hypopharyngeal cancer. Twenty-three patients with esophageal or hypopharyngeal cancer were studied over 2 weeks. Ten of them received magnesium supplementation and 13 did not. Magnesium sulphate(20 mEq) was administered before 5-fluorouracil(800mg/m2/24 h/day 1-5)and cisplatin(80mg/m2/day 1)(FP)treatment. The maximum serum creatinine concentration of magnesium-supplemented group demonstrated a significantly lower concentration compared to the non-magnesium-supplemented group(p=0. 018). As a result, magnesium supplementation successfully reduced the incidence rate of nephrotoxicity(p=0. 038). These results showed that magnesium supplementation before FP treatment may be quite beneficial for preventing nephrotoxicity in patients with esophageal and hypopharyngeal cancer, and it is therefore recommended that magnesium be routinely supplemented during FP treatment for esophageal or hypopharyngeal cancer.