Purpose: Flaxseed (Linum usitatissimum L.) is a widely consumed functional food rich in omega-3 fatty acids, lignans, and fiber. However, due to its cyanogenic glycoside content, excessive consumption may lead to toxic effects. This study aimed to evaluate the histopathological effects of high-dose oral flaxseed administration on rat lung tissue.Materials and Methods: Thirty-two adult female Wistar Albino rats were randomly divided into four groups (n=8 each): Control, Low Dose (1.4 g/kg/day), Medium Dose (2.8 g/kg/day), and High Dose (5.6 g/kg/day). Flaxseed was administered via oral gavage for seven days. At the end of the experiment, the rats were sacrificed under anesthesia. Lung tissues were fixed in 10% neutral for-malin, stained with H&E, and examined under light microscopyResults: No pathological changes were observed in the control and low-dose groups. In the medium-dose group, vascular congestion was noted. The high-dose group exhibited vascular congestion, mononuclear cell infiltration, and interalveolar septal thickening. These findings indicate that flaxseed administration induces dose-dependent inflammatory and structural alterations in lung tissueConclusion: Short-term high-dose flaxseed intake causes significant histopathological changes in rat lung tissue. Findings such as vascular congestion, inflammatory infiltration, and septal thickening suggest potential pulmonary toxicity. The absence of similar findings at lower doses supports a dose-dependent relationship. These results emphasize the need for cautious use of functional herbal products and encourage further biochemical and molecular studies to elucidate underlying mechanisms.