The present study has been designed to evaluate the possible nephrotoxicity of the angiotensin converting enzyme inhibitor, captopril on renal tubules of adult and maternally treated fetuses of CD-1 mice. The study included the effect of captopril administration for one month up to three months in adults, while in fetuses, they were exposed to the drug through their mothers in two periods. The first was from 6th-12th days of pregnancy, while the second was from 6th -18th day of pregnancy. The dose used in the present study represents the dose equivalent to the therapeutic daily dose taken by human. All the recorded tissue damage was found to be time dependent. The first remarkable feature noticed in all the treated adult animals was the presence of hyaline casts that obstructed most of the renal tubules. The second remarkable feature was the increase of the intertubular space associated with irregularity of the tubules due to the degeneration and vacuolation of the basal regions of the cells. Renal tubule cells showed large blebs, accumulaton of lipids, degeneration and necrosis. In maternally treated fetuses, the proximal convoluted tubule cells displayed moderate vacuolation and marked increase of lysosomes while some of the distal convoluted tubules revealed atrophy and their cells showed loss of mitochondria. In addition, the collecting tubules showed loss of microprojections. Worthy to mention that there was apparent increase of mesenchymal cells as well as fibroblasts in the fetuses maternally treated with captopril. The significance of these changes was discussed and it should be emphasized that captopril must be taken with caution for pregnant women and those who suffer from renal troubles. Moreover, kidney function should be monitored during therapy .