Bleomycin (BLM), a chemotherapeutic agent is indicated in the management of some types of cancers. This drug produces a dose-dependent pulmonary fibrosis (PF) in most patients as well as experimental animals through oxidative injury. This study aimed to investigate the effect of gallic acid (GA), a polyphenolic compound, against PF-induce by BLM in rats. The rats were given GA orally at doses (50, 100, and 200 mg/kg/day) for 7 consecutive days before the administration of single intratracheal (it) instillation of BLM at 7.5 IU/kg. GA doses were continued for 21 days after BLM exposure. The regulatory effects of GA on BLM-induced pulmonary toxicity were determined by assaying oxidative stress biomarkers, lung and serum cytokine levels, and by histopathological examination of lung tissue. The results showed that intratracheal BLM administration significantly increased the inflammatory or fibrotic changes, collagen content, levels of malondialdehyde (MDA), and pro-inflammatory cytokines such as TNF-α and IL1β in lung. Also, it significantly decreased non-enzymatic (total thiol) and enzymatic (glutathione peroxidase (GPx)) antioxidant contents in the rats' lung tissue. However, oral administration of GA reversed all of these biochemical indices as well as histopathological alterations induced by BLM. Results of the present study demonstrate that GA, by its antioxidant properties, attenuates oxidative damage and fibrosis induced by BLM. Thus, an effective supplement with GA as an adjuvant therapy may be a very promising compound in reducing the side effects of BLM.