One of the widely used gastrointestinal drugs is bismuth oxide, which is used in the treatment of bacterial infections, especially those caused by Helicobacter pylori, the main causative agent of stomach ulcers. In addition to this drug, bismuth has numerous applications in the cosmetics, metallurgy, and other industries. Alongside these extensive applications, the toxicity of bismuth is under investigation. In this study, NMRI mice were divided into 3 groups. Groups 1 and 2 were gavaged with bismuth oxide nanoparticles at concentrations of 200 and 800 mg/kg, respectively, and group 3 served as the control group and was gavaged with normal saline for 30 days. After dissection, blood sera were separated and blood factors related to the liver (ALT and AST) and kidney (urea and creatinine) were measured. The results showed that the levels of ALT and AST in the serum of both bismuth groups increased compared to the control group, but the amount of change in urea and creatinine was not significant compared to the control group. ALT and AST are biological markers of the liver that are released into the bloodstream in case of liver damage. As a result, bismuth was able to increase their serum levels while causing liver damage. Urea and creatinine are excreted through the kidneys, and when kidney function is impaired, their serum levels increase as the glomerular filtration rate decreases. This was not observed in our study, and it is suggested that the liver and kidneys be examined histopathologically in future studies to investigate the potential effects of this substance more accurately.