1. Two experiments were conducted to evaluate the effects of early feed restriction on the lipid peroxidation，pulmonary vascular remodeling and ascites incidence in broiler under normal and low ambient temperature. 2. In experiment 1, the restricted birds were fed 8 hours per day either from 7 to 14 d or from 7 to 21 d, while the controlled birds were fed ad libitum. In experiment 2, the restricted birds were fed 80% or 60% of previous 24 hour feed consumption of full-fed controls for 7 days from 7 to 14 d. On d 14, half of the birds in each treatment both in experiment 1 and experiment 2 were exposed to low ambient temperature to induce ascites. 3. Body weight and feed conversion ratio were measured weekly. The incidences of ascites and other disease were recorded to determine ascites morbidity and total mortality. Blood samples were taken on d 14, 21, 28, 35 and 42 to measure the plasma malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) levels. On d 42, Samples were taken to determine the right/total ventricular weight ratio (RV/TV), vessel wall area/vessel total area ratio (WA/TA) and mean media thickness in pulmonary arterioles (mMTPA). 4. The results showed that low temperature treatment significantly increased the plasma MDA concentration. When broilers were exposed into cool environment for 3 weeks, the plasma SOD and GSH-Px activity were decreased compared with normal temperature treated chicks. The RV/TV, WA/TA and mMTPA on d 42 were significantly increased in birds exposed to cold in line with the increased pulmonary hypertension and ascites morbidity. Early feed restriction markedly decreased the plasma MDA concentration. The plasma SOD and GSH-Px activity of feed restricted birds were markedly higher than that of the fed ad libitum on d 35 and d 42. All early feed restriction treating reduced ascites morbidity and total mortality. On d 42, the RV/TV, WA/TA and mMTPA of feed restricted broilers were lower than that of the uncontrolled broilers. 5. The results suggested that early feed restriction alleviated the lipid peroxidation, promoted the activity of enzymatic antioxidant and inhibited pulmonary vascular remodeling. These changes might be associated with reduced ascites incidence.