Introduction: Renal development involves 2 basic processes: morphologic formation and acquisition of function. Aim of the Work: The aim of the present study was to obtain histological information about the postnatal development of the filtration barrier and to throw more light upon the concomitant developmental changes of the convoluted tubules in albino rat’s renal cortex. Materials and Methods: Ten pregnant female rats were utilized. Fifteen of their offsprings were taken and divided into 3 groups: Group A: studied at the 2nd day postnatal. Group B: studied at the 10th day postnatal. Group C: studied at the 21st day postnatal. Kidneys were removed then 5µm thick paraffin sections were obtained and stained with haematoxylin and eosin stain for light microscope study. Renal cortex was cut into minute pieces and prepared for electron microscope study. Results: Light microscope examination of 2 days renal cortex exhibited two cortical zones. The subcapsular zone contained immature forms of the renal developmental stages; the juxtamedullary zone contained mature renal corpuscles. While, electron microscope examination showed podocytes with flat cytoplasmic sheets and foot processes. Endothelial cells had few fenestrations. The filtration barriers revealed double basement membrane. The lining cells of proximal tubules had few short apical microvilli, mitochondria randomly oriented and few basal infoldings. Also, those of distal convoluted tubules appeared with randomly oriented mitochondria and some basal infoldings. The light microscope examination of 10 days renal cortex showed disappearance of all immature forms and maturing glomeruli were observed. Electron microscope examination showed podocytes with its primary processes and foot processes. The endothelial cells showed numerous fenestrations. The filtration barriers revealed fused basement membranes with presence of outpockets. The lining cells of proximal tubules had numerous tall tightly packed apical microvilli,. Mitochondria appeared lodged in the basal infoldings in both proximal and distal tubules. The light microscope examination of 21 days renal cortex revealed mature renal corpuscles with lobulated glomeruli. Electron microscope examination demonstrated mature glomeruli showing podocytes with numerous foot processes. The filtration barrier showed regular basement membrane with no outpockets. The endothelial cells appeared attenuated with numerous fenestrations. Proximal and distal tubules showed mature picture. Conclusion: It has been proposed that adult renal diseases may be determined by events that occurred during fetal development. Therefore, results of studies on renal development in experimental models need to be interpreted and correlated carefully with the concomitant functional changes