The free radical scavenging ability, metal ion chelation ability and reducing ability of different concentrations of placenta peptide from Tibetan sheep were determined, and the distribution of relative molecular weight, amino acid composition and structural characterization were also investigated to explain the causes of antioxidant capacity. The results showed that the antioxidant capacity of sheep placenta peptide was positively correlated with its concentration, and it had strong radical scavenging ability for DPPH· and ·OH with IC₅₀ of 2.83 mg/mL and 0.94 mg/mL, respectively, which were comparable to BHT. In addition, the placenta peptide from Tibetan sheep also had certain O ·scavenging ability, metal ion chelating ability for Fe²⁺ and reduction ability for Fe³⁺and Cu²⁺. Moreover, the placenta peptide below 1 000 Da of molecular weight accounted for nearly 90% in total peptide, which contained an abundance of aspartic acid, glutamic acid, glycine and so on. Structural characterization results showed that the placenta peptide still remained the proper functional group structures of protein in sheep placental, the micromorphology of dense spherical granular happened, and the rearranged protein molecules aggregated during degradation of proteins to peptide. Based on the results of circular dichroism, the decreased content of α-helices, increased content of β-sheets and random curl were observed. In a word, the placental peptide from the Tibetan sheep have nice antioxidant capacity due to its appropriate content of oligopeptides and amino acids profile, special micromorphology properties and space structure.