A total of 211 Chilean jack mackerel (Trachurus murphyi) were collected by a large scale trawler named “KAIXIN” from July to October 2010 in the southeast Pacific Ocean. The morphologic features of their sagittas were observed and measured. The sagittas of Chilean jack mackerel have four parts: front part, back part, dorsal part and ventral part. It has an apparent rostrum which is longer than the antirostrum. The result of principal component analysis on 24 morphologic indices shows that the total sagitta length (L₁), distance from the core to the end(L₃), distance from the end to the antirostrum(L₁₁) and distance from the end to the intersection(L₁₃) can reflect the length features of sagitta, and distance from the core to the ventral(L5), distance from the end to the ventral(L₁₀), distance from the ventral to the intersection(L₁₈) and antirostrum length(L₂₃) can reflect its width features. The relationships between the featured length of sagitta including L₁, L₃, L₁₁ and L₁₃, and fork length as well as body weight were best described by power functions(P=0 <0.05). Also, the relationships between the featured width of sagitta including L₅, L₁₀ and L₁₈, and fork length as well as body weight were best described by power functions(P=0<0.05). Antirostrum length (L₂₃) was best described by exponential functions with fork length as well as body weight (P=0<0.05).