The critical period during which maternal hyperglycemia predisposes offspring to develop reproductive disorders in adult life is not known. The relationship between maternal hyperglycemia at different stages and reproductive functions of male offspring was investigated. A single intraperitoneal injection of alloxan (90 mg/kg body weight) was administered at gestation days (GD) 1, 8 and 15. Animals were subsequently given 10% glucose solution daily as drinking water until parturition. All male pups were sacrificed on the 63rd day of postnatal life. Birth weight, anogenital distance index (AGDi), testes descent day, preputial separation day, sperm profile, serum testosterone, luteinizing hormone and follicle-stimulating hormone levels and the histology of the testis were assessed. Data significance test was based on 95% confidence interval. GD1 pups showed a significant increase in mean birth weight, whereas GD8 pups and GD15 pups had significantly reduced birth weight as compared with control. AGDi was significantly increased in GD8 and GD15 pups. Testes descent and preputial separation in all the experimental groups were significantly earlier. There was a significant reduction in sperm count and viability in GD8 offspring. Sperm motility was reduced in all test groups. Testosterone level was reduced in all test groups. Histology of the testis showed varying degrees of pathologies. It was deduced from this study that maternal hyperglycemia caused alterations in reproductive functions in male offspring of Wistar rats irrespective of the period of gestation involved, although GD8 pups were most severely affected.