Few studies are available about the role of dietary zinc (Zn) in respiratory diseases. Adult male rats were divided into 2 groups and fed respectively a moderate Zn-deficient diet and a Zn-adequate control diet. In lung tissue at 2 months, thiobarbituric acid-reactive species (TBARS), total glutathione, glutathione disulfide, protein carbonyls, metallothionein, and the activities of glutathione peroxidase (GPx), catalase, CuZn-superoxide dismutase (CuZnSOD) and glucose-6-phosphate dehydrogenase (G-6-PDH) were increased, but protein thiols decreased. In lung tissue at 4 months, TBARS, metallothionein, and the activities of CuZnSOD, Mn-superoxide dismutase (MnSOD) increased. The activities GPx, catalase, G-6-PDH were lower than control group. The changes were accompanied by histological alterations in Zn-deficient lung. The results provide evidence of the pro-oxidative effects of Zn-deficiency in lung, and suggest that the time of treatment play a key role in determining lung susceptibility to oxidative stress.