Background: Aspartame is a widely employed synthetic sweetener used in diet control and by diabetic patients. Its safety based on the findings of the previous studies showed controversy. Aim of the Work: The aim of this study was to demonstrate the chronic effect of aspartame on the structure of the kidney in the newborn, adult and old albino rats. Materials and Methods: In this work, 60 albino rats were used, 40 of which were three month old, while the remaining 20 rats were twelve month old at the beginning of the study. They were divided into 3 groups: A, B, C and every group was subdivided into 2 subgroups; control and treated. Group A included 20 female albino rats aged three months. The treated subgroup A received aspartame in a dose of 20 mg/kg/day dissolved in tap water through an intragastric tube for three months pregestational and during the gestational period. The offspring numbers, body and kidney weights were estimated and statistically analyzed and their kidneys were examined histopathologically. Group B included 20 adult albino rats aged three months. Group C included 20 albino rats aged twelve months. The treated animals of groups B and C were given aspartame in the same dose and by the same route as in group A for six months. The kidney specimens from all groups were processed for light microscopic examination using Haematoxylin and Eosin stain. Toluidine blue stain was used for the semithin sections of the adult rat's kidney specimens. Electron microscopic study of the proximal convoluted tubules of the adult kidney was done. Results: The results of this study revealed a delayed development of the kidney of the newborn rat with the maternal aspartame administration in addition to degenerative changes in the renal corpuscles and tubules. The statistical analysis of the newborns' body and kidney weights showed significant reduction. The kidneys of aspartame-treated adult rats showed degenerative changes affecting the renal corpuscles and tubules. The renal corpuscles had shrunken glomerular capillary tuft and widened Bowman`s space. Some of which revealed irregularity of Bowman`s capsule. The renal tubules showed dilatation of the tubular lumen, dense nuclei and vacuolated cytoplasm with sloughed epithelial lining cells. Congested and dilated blood vessels were also observed. The ultrastructural study of the proximal convoluted tubular lining cells revealed an extensive damage of the cytoplasmic organelles and the brush border. Aspartame-treated aged rat's kidney showed massive degenerative changes in comparison to the other treated groups. All the renal tubules showed thinning of their lining epithelium with dilated lumen. Some of which had destructed or thickened basement membrane. Others showed accumulation of dense acidophilic casts inside the lumen. Dilated and congested blood vessels with vacuolated cytoplasm were noticed. Conclusion: It was concluded from this study that aspartame had nephrotoxic effects on the newborn, adult and aged rats.