Diabetes Mellitus is characterized by chronic hyperglycemia and associated with an increased production of reactive oxygen species (ROS). Oxidative stress is the result of accumulation of free radicals in tissues which specially affects beta cells in pancreas. Glutathione S-transferases (GSTs) are a family of antioxidant enzymes that include several classes of GSTs. These enzymes have important roles in decreasing of ROS species and act as a kind of antioxidant defense. To investigate the association between GSTs polymorphism with type 2 diabetes mellitus (T2DM), we investigated the frequency of GSTM1, T1 and P1 genotypes in patients with T2DM and controls. The genotypes of GSTT1, M1 and P1 were determined in 171 clinically documented T2DM patients and 169 normal cases (as controls) by multiplex polymerase chain reaction and PCR-RFLP. In diabetic patients, the frequency of GSTM1-null genotype was significantly (OR = 1.74; 95 % CI = 1.13-2.69, P = 0.016) higher than that in control. However, the frequency of GSTT1 (OR = 1.29; 95 % CI = 0.07-2.14, P = 0.367) and GSTP1 (OR = 0.83; 95 % CI = 0.53-1.30, P = 0.389) genotypes were not significantly different comparing both groups. Also, the frequency of both GSTT1-null and GSTM1-null genotypes in patients (19.88 %) was significantly higher compared to controls with the same genotypes (11.83 %, P = 0.022). Our results indicated that GSTM1 and GSTT1 genotypes might be involved in the pathogenesis of T2DM in south Iranian population.