The objective of this study was the evaluation of aspartame effects on morphometric alterations of the glomerulus, proximal and distal convoluted tubules and collecting ducts of the rat fetal kidney during organogénesis. Fifteen pregnant rats averaging 24 g body weight, were divided into 3 groups (n=5 each) of controls, rats treated with aspartame exposed to room temperature and rats treated with aspartame heated to 40°C. Animals were given 14mg / kg aspartame by the intragastric route on the 9th, 10th, and 11th days of pregnancy. Karyometric and stereological techniques estimated morphological changes. A significant decrease of fetal body weight was observed in the group given aspartame kept at room temperature, compared to controls. Karyometry permitted the estimation of the significant nuclear variations observed in the cells of the glomerulus, proximal and distal convoluted tubules and collecting ducts of aspartame-treated rat fetuses. Stereolgical parameters showed statistically significantly increased cell volume and decreased numerical cell density in fetal kidneys of rats treated with aspartame heated to 40° compared to controls. These results indicate that the use of aspartame leads to alterations in all renal structures studied, suggesting this product's nephrotoxicity