Background  and  Objective:  Favipiravir  is  associated  with  more  serious  side  effects  at  higher  doses.  This  experimental  study proposed  to  investigate  the  effect  of  favipiravir  on  dose-dependent  lung  toxicity  in  rats  biochemically  and  histopathologically. Materials and Methods: The rats were divided into four groups as healthy (HG), 100 mg/kg favipiravir (FAV-100), 200 mg/kg favipiravir (FAV-200) and 400 mg/kg favipiravir (FAV-400). Favipiravir 100, 200 and 400 mg/kg doses were administered by oral gavage to the other groups except HG. To the HG group, only distilled water (0.5 mL) was applied in the same way. This procedure was repeated twice a day for a week. Then, the rats were euthanised with high-dose anaesthesia and lung tissues were removed. Oxidative stress parameters such as malondialdehyde (MDA), Total Glutathione (tGSH), superoxide dismutase  (SOD),  total  oxidant  status  (TOS)  and  total  antioxidant status (TAS) were examined. After the one-way ANOVA, the Tukeyʼs post hoc  test was performed. Results: Favipiravir dose-dependently increased MDA and TOS also decreased tGSH, SOD  and  TAS  in  rat  lung  tissue.  As  favipiravir  was  given  in  increasing  doses,  it  was easier  to  observe  the  changes  between  the  different  groups.  This  was  also  supported  by  the  histopathological  data. Histopathologically, interstitial pneumonia and lymphoid hyperplasia were mild in the 100 mg/kg favipiravir group, severe at high doses. Conclusion: As the dose of favipiravir increased, oxidant levels increased and antioxidant levels decreased in the lung tissue. In line with these results, it was observed that favipiravir caused a dose-dependent pulmonotoxic effect in rats.