The aim of this study was to investigate arginase activity, total oxidant capacity (TOC), total antioxidant capacity (TAC), and oxidative stress index (OSI) in cows with lung cystic echinococcosis (CE). The subjects were 20 cows with lung CE (parasitized group) and 20 healthy cows (control group). A significant increase in arginase activity, TOC, and OSI, and a significant decrease in TAC were found in the parasitized group compared with the control group (P < 0.001). Histopathological examination revealed a fibrous tissue reaction with inflammatory cell infiltration surrounding the CE in the lungs. The study revealed that increased arginase activity, TOC, and OSI levels and decreased TAC levels occurred in lung CE in cows. Increased arginase activity may be an important parameter for pulmonary fibrosis associated with lung CE in cows. Oxidant production due to chronic inflammation, as evidenced by the increased OSI levels, might contribute to persistent lung injury.