Background: Renal development involves two basic processes: morphologic formation and acquisition of function. COX-2 expression during development indicates potentially important roles for COX-2 metabolites in glomerulogenesis. Aim of the work: This work aims to study the prenatal and postnatal developmental changes of the renal cortex of the albino rats and to assess relationship between COX-2 and renal morphogenesis using light microscopy and Immunohistochemical study. Material and methods: 25 virgin female and 10 male Wister albino rats were obtained from the animal house, Faculty of Medicine, Zagazig University and were used in this study. Mating was allowed overnight and the process was repeated until all females became pregnant. The pregnancy of 6 rats was terminated at the gestational ages (16, 20) days respectively and the fetuses were considered as the prenatal (group A) which were subdivided according to gestational age into: Subgroup A1: at the embryonic day 16 (ED 16) and Subgroup A2: at the embryonic day 20(ED 20). The remaining rats were allowed to continue the pregnancy. The offsprings of 15 pregnant albino rats were considered as the postnatal(group B) and then subdivided into Subgroup B1: studied at postnatal day2 (PD2). Subgroup B2: studied at postnatal day 7 (PD7).Subgroup B3: studied at postnatal day 14 (PD14). Subgroup B4: studied at postnatal day21 (PD21). The offsprings of the remaining rats were allowed to live 6 months under observation and were used as the adult group (group C). The kidneys were removed and processed for light microscope and Immunohistochemical examination. Results: The adult rat renal cortex showed normal architecture with a homogenous appearance as it was densely packed with glomeruli with no differentiation into zones. In 16 days albino rats embryo, the kidney revealed differentiation into cortex containing condensed mesenchyme and medulla containing undifferentiated mesenchymal tissue. In 20 days albino rats embryo, both the superficial and deep parts of the renal cortex featured a nephrogenic mesenchymal region containing immature forms of renal developmental stages. Glomeruli in the deep part were observed to be further developed than those in the superficial part of the renal cortex. Light microscopic examination of the kidneys of all postnatal groups revealed that the juxtamedullary nephrons were only developed at birth and the renal cortex acquired maturation in a centrifugal manner with the superficial nephrons were the last to mature. Renocortical COX-2 expression was elevated in immature kidney, rat kidney maximal expression of COX-2 protein has been observed on post day 7, post day 14 and then declined gradually during postnatal development compared with P14. The pattern of COX-2 expression was originally apparent in the juxtamedullary region gradually moved further out in the cortex. Kidney COX-2 was expressed in the macula densa and thick ascending limb of Henle Conclusion: We concluded that, the juxtamedullary nephrons developed at birth and the renal cortex acquired maturation in a centrifugal manner with the superficial nephrons were the last to mature by postnatal day 21(PD21).The renal cortical COX-2 expression was developmentally regulated. As selective inhibitors of COX-2 become available, it will be important to assess their effects on renal morphogenesis