Abstract:Stable isotope in the beaks has become a good material for ecological study of cephalopod as the characteristic of single structure and incorrosiveness. In this study, the stable isotopes of beak and its relationship between mantle length, age and sexual maturity were analyzed based on the samples of Dosidicus gigas collected by Chinese jigging vessel during July to August in 2009. The results showed that the mantle length of samples ranged from 25.6 to 35.8 cm, body weight ranged from 447.6 to 1 122.3 g,and these samples belonged to small group. The values of δ13C and δ15N of lower beaks was higher than upper beak, but the difference was not significant (P>0.05). The values of δ13C and δ15N increased by mantle length and age, their relationships were fitted by the linear model. The values of δ13C and δ15 N were variable with different sexual maturity stage, and the sample with stage Ⅲ has the maximum value of δ13C and δ15 N. The results indicated that its habitat shifted from the continental shelf to the ocean and the scope of activities of Dosidicus gigas gathered toward more productive waters from the changes of δ13C and δ15N during the growth process of Dosidicus gigas. At the same time, the changes of δ13C and δ15 N were closely related with sexual maturity and individual growth process. It is recommended that the stable isotope of the beak and other hard tissues and its different parts should be studied combined with marine plankton in the studying area in order to provide a basis to understand and master the ecology of Dosidicus gigas in the future.