Background: Gibberellic acid (GA3) is one of naturally occurring plant growth regulator, it is one of the family of "biocides" that are phyto-hormones with insecticidal effects. Most of nitrogenous wastes are eliminated through the two kidneys that in addition maintains blood volume, composition and pressure and keeps bone density. Aim: To evaluate the histopathological effect GA3 on rat’s renal cortex postnatally in different ages (PND1, PND 7 & PND 21). Material &Methods: Pregnant female albino rats (n=20) had been distributed into: control group and treated group, GA3 was administered from the 14th day of pregnancy to the 21st postnatal day at a dose of 55 mg/kg of body weight /day. After giving birth, the male pups of each group were randomly divided into three subgroups and were sacrificed at the (1 day), (7 days) and at (21 days). Animals were anaesthetized and sacrificed. Kidneys of pups born to control and treated mothers were obtained and processed for examination of oxidative stress marker, histological and immunohistochemical examination. Results: pups of GA3 treated mothers showed increase in urea, creatinine serum level and MDA level and decrease in CAT and GPX content. Moreover, histological examination of the kidneys of these pups revealed multiple atrophied immature forms of glomeruli, multiple congested blood capillaries, some renal tubules showed loss of some cells lining them and others with vacuolated cytoplasm. Statistically, GA3–treated groups at all age groups displayed a highly significant decrease in the mean cortical thickness than control groups. Moreover, the area percentage of collagen and of renal PCNA expression showed a significant increase with GA3 treatment of mothers. Conclusion: Exposure of pregnant rats to GA3 in late pregnancy and during lactation induced oxidative stress and histopathological alterations in renal cortex of suckling pups.