To explore the impact of sulfur (S) fertilization on copper (Cu) metabolism in grazing Tibetan sheep, fertilizing and grazing experiments were conducted in the Southwest Grand Grassland, China. The tested pasture was randomly divided into four parts by the fencing device (2 hm²/part). The pasture received ammonium sulfate [(NH₄)₂SO₄] treatment in summer in 2020 (0, 300, 400, and 500 kg/hm² for part I, part II, part III, and part IV, respectively). 24 Tibetan sheep (one year old) were randomly divided into four groups, and assigned to the selected pastures (part I, part II, part III, and part IV for group I, group II, group III, and group IV, respectively). The grazing experiments lasted for 90 days. The results showed that the contents of nitrogen (N) and S in fertilized forage were markedly higher than those in unfertilized grass (P<0.01), but there was no significant difference among fertilized forages. The contents of Cu in blood and liver in the Tibetan sheep from fertilized pasture were extremely lower than those in animals from unfertilized pasture (P<0.01). The contents of Hb and PCV in the tested sheep from fertilized pasture were extremely higher than those in sheep from unfertilized pasture. The activities of serum SOD, GSH-Px, T-AOC, Cp, and CAT in sheep from fertilized pasture were extremely lower than those in sheep from no fertilized pasture (P<0.01), but there were no obvious differences among the Tibetan sheep from fertilized pasture (P>0.05). The contents of MDA in the Tibetan sheep from fertilized pasture were significantly higher than those in animals from no fertilized pasture (P<0.01). There was no obvious difference among the Tibetan sheep from fertilized pasture (P>0.05). Therefore, (NH₄)₂SO₄ fertilization not only greatly influenced the contents of S and N in forage, but also extremely decreased Cu contents of animal tissues in the Tibetan sheep from fertilized ranges.