The generation of reactive oxygen species in diabetes is considered to be the major cause for the mutation related defects such as cancer, infertility etc. Glimepiride (Gmp) is a third generation antidiabetic sulphonylurea known to possess the antioxidant effect in streptozotocin (STZ) induced diabetes. In this study, the anti-mutagenic activity of Gmp (0.175, 17.5 and 175 mg/kg, po daily for 4 weeks) was evaluated against the nicotinamide (NA-230 mg/kg) and STZ (65 mg/kg) induced somatic and germinal cells defect using bone marrow micronucleus (MN) test and sperm abnormality test respectively in male Wistar rats. Administration of Gmp at 175 mg prevented the NA-STZ induced increased frequency of MN in polychromatic and normochromatic erythrocytes. The treatment with Gmp also decreased the sperm shape abnormality and enhanced the sperm count besides improving the antioxidant status in the diabetic rats. However, the other doses of Gmp (0.175 and 17.5 mg) did not produce significant change in the MN frequency and sperm abnormality although Gmp at 17.5 mg showed significant antidiabetic effect in the hyperglycemic animals. The results indicated that Gmp inhibited the NA-STZ mediated changes in the MN frequency and sperm abnormality and enhanced the antioxidant defense. The observations suggest that the antioxidant property of Gmp could have contributed for its ability to decrease the NA-STZ mediated defects in somatic and germinal cells.