Introduction: Triolein used as a plasticizer, a lubricant, and present in cocoa butter. Its occupational exposure led to health hazards especially lung injury. Hesperidin antioxidant flavonoid is present in many fruits and vegetables.

Aim of the Work: The present research aimed to evaluate the possible ameliorative effect of hesperidin on triolein-induced lung structural changes in rats using histological and immunohistochemical study.

Materials and Methods: 45 adult male albino rats were used. They were divided into Group I: (control group). Group II: rats were received 0.2 ml triolein then were sacrificed after 21 days. Group III (triolein and hesperidin): rats subdivided in 2 subgroups: IIIa, IIIb, received triolein as group II . and simultaneously received hesperidin 50 mg/kg/day by gavage for 21, 28 days respectively.

Results: Group II showed marked affection of lung tissue. The bronchiolar epithelium showed dark-stained nuclei and vacuolated cytoplasm, desquamated epithelial cells. The alveoli were collapsed with thickened interalveolar septa. The interstitial tissue showed congested blood vessels, inflammatory cellular infiltration, and extravasated blood in H&E-stained sections. Group II also showed increased deposition of collagen fibers, increased expression of alpha –Smooth muscle actin (α-SMA) in the interalveolar septa, wall of the blood vessels and bronchioles. Group IIIa, IIIb showed improvements of the previous pathological findings with more improvement in group IIIb

Conclusion: hesperidin could protect the lung from the injurious effect of triolein possibly due to its anti-inflammatory, antioxidant and antifibrotic actions.