Letrozole (LTZ), is an aromatase inhibitor, that has been widely used in a variety of diseases such as polycystic ovary syndrome, endometriosis, and breast cancer. LTZ is received via the oral route and metabolized in the liver. Therefore, LTZ may have toxic effects like other drugs metabolized in the liver. Based on this, our study aimed to investigate the effect of LTZ on liver function and biochemical parameters. For this purpose, 16 Wistar albino female rats were divided into two groups (n=8): Control and LTZ respectively. The rats in the letrozole group were administered with 2 mL/kg LTZ by oral gavage once a day for 21 days. The Control group received the vehicle once a day for 21 days. Blood samples were collected on the 22nd day of the experiment. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (GGT), lactate dehydrogenase (LDH), albumin (ALB), alkaline phosphatase (ALP), direct bilirubin and total bilirubin were measured. Biochemical analysis indicated that ALT, AST, LDH, ALP, and total bilirubin levels were significantly higher in the LTZ administrated group compared to the Control. ALB levels decreased in the LTZ group. In conclusion, it was determined that LTZ has toxic and detrimental effects on the liver. We suggested that long-term LTZ administrated patients should be under control against liver damage and may have liver supporting adjuvant therapies for robust liver functions.