Aspartame is a common artificial sweetener that is thought to be dangerous. On the other hand, stevioside (stevia) a natural sweetener of plant origin was assumed to be a natural alternative to artificial sweeteners. This study aimed to determine whether aspartame or stevioside affected biochemical, serum-biochemical, and immunohistochemical changes in adult rats following six weeks of exposure. Forty-eight rats were used and divided into three groups: Group I: the control group, Group II: rats received aspartame (75 mg/kg/day), Group III: rats received stevioside (45 mg/kg/day). All medications were given orally for 6 weeks. Lipid Peroxidation product (MDA); liver glutathione (GSH); nitric oxide (NO); Liver Superoxidase dismutase activity(SOD); catalase (CAT), Low-density lipoprotein (LDL); very low lipoprotein (VLDL); the cholesterol in the HDL; Alanine Aminotransferase (ALT), and Aspartate Aminotransferase (AST); Creatinine, Urea, Total proteins were assessed in blood and liver tissue specimens. In addition, hepatic histopathological and immunohistochemical investigations were done. The Aspartame group showed a significant increase in most of the investigated biochemical parameters (especially glucose, MDA, liver NO, LDL, VLDL, ALT, AST, creatinine, and urea) with a significant decrease in serum albumin and the endogenous antioxidants (GSH, SOD, CAT) compared to the control group while stevia-exposed animals showed a significant decrease in the same biochemical parameters with a significant increase in the same endogenous antioxidants. Moreover, severe histopathological and immunohistochemical changes were observed in the liver of Aspartame- treated animals. However, Stevia-treated rats showed the least changes. Therefore, it can be concluded that Stevia was less harmful than aspartame.