Nettle () contains a wide range of chemical constituents that confer a strong antioxidant capacity to the plant. The present study was to investigate the antioxidant gene expression and pulmonary hypertensive responses of broiler chickens to . A total of 240 one-d-old broilers (Ross 308) were randomly assigned to 4 dietary levels of (0, 0.5%, 1% and 1.5%). Birds were reared for 6 wk in a high altitude region (2,100 m). The results showed a significant relative overexpression (target gene/β-actin as the arbitrary unit) of catalase () and superoxide dismutase 1 () in the liver and lung of the chickens fed Lipid peroxidation was significantly suppressed, as reflected in reduced circulatory concentrations of malondialdehyde (MDA) in the birds fed . These birds also had significantly ( < 0.05) higher serum nitric oxide (NO) concentrations than those in the control group. Feeding at 1% and 1.5% also attenuated the right ventricular hypertrophy (reflected in the lower right to total ventricular weight ratio), which was associated with a significant lower rate of mortality from pulmonary hypertension syndrome. Feeding led to an upregulation of hepatic and pulmonary antioxidant genes.