Pancreatic β cells are more sensitive to cytotoxic stress than several other cells due to the expression of very low levels of antioxidant enzymes. Glutathione-S-transferase (GST) is a detoxification enzyme essential for a cellular protection against oxidative damage. Thus, the objective of this chapter is to verify the impact of the hypothesis of all effects of Glutathione S-transferase polymorphism in patients with diabetic complications. Diabetic nephropathy (DN) is the main secondary complication of diabetes mellitus (DM). Notably, the expression of GST genes has been described in different variations as ethnic populations. Some studies have suggested association between genetic polymorphism for GSTM1, GSTT1 and GSTP1 and DN, but others do not. The results are still inconsistent and, therefore, more studies are needed to be performed.