Based on seasonal sampling in the Beibu Gulf (Tonkin Gulf), South China Sea, from August 2010 to May 2011, biological characteristics such as growth, reproduction, and ingestion of 2,179 mitre squid, Uroteuthis chinensis, were investigated. The results showed that the maximum and minimum mantle lengths of U. chinensis were 438 mm and 49 mm, respectively, whereas the corresponding body weights were 723 g and 7.3 g, respectively. Both mantle length and body weight peaked in spring. The relationship between mantle length (L, in millimeters) and body weight (W, in grams) was W = 1.43 × 10^-3 × L^2.19 (R² = 0.92), and between mantle length and gutted weight (W, in grams) was W = 1.04 × 10^-3 × L^2.24 (R² = 0.97). The number of females was equal to that ofmales, with a sex ratio of 1:1.01. Furthermore, no obvious seasonal change was observed. There was no stage VI of gonad maturation, and stage I was dominant year-round. The feeding intensity was low and the empty stomach rate was high throughout the year. The mean trophic levels from spring to winter were 3.6, 2.7, 3.0, and 3.3, respectively. The results indicated considerable differences in the sampling areas. In addition, seasonal changes in catch and distribution were observable whereas biomass varied greatly.