During July-November in 2003, pelagic fish survey was conducted by longliner covering areas of 03°S-17°S , 96°W-146°W. Sampling gear was longline fishing. With the precaudal length increment, the total gonad weight of male blue shark increases greatly but that of female increases little. The average value of TGSI(total gonadosomatic index) of female amounts to 0.64 but male increases to 0.98. The blue shark is viviparous and the period of parturition appears in Oct.-Nov. The sex ratio of adult blue shark is not fitted to 1:1. Preliminary results show that female matures at total length 183 cm(precaudal length 137cm). The broods range from 13 to 62 and average 34.29±11.2 (n=28). There is no obvious relationship between broods and maternal length. The length at birth arrives at total length 44cm. Based on the observation of egg diameter in the ovary of female blue shark, the maximum of egg diameter is 16-18 mm occurred in Nov. and at the same time fertilized eggs appear. Based on the clasper length analysis, the smallest male matures at total length 174 cm (precaudal length 131 cm). During July-November in 2003, pelagic fish survey was conducted by longliner covering areas of 03 ° S-17 ° S, 96 ° W-146 ° W. Sampling gear was longline fishing. With the precaudal length increment, the total gonad weight of The blue shark is viviparous and the period of parturition appears in Oct.-Nov. The sex ratio of adult blue shark is not fitted to 1: 1. Preliminary results show that female matures at total length 183 cm (precaudal length 137 cm). The broods range from 13 to 62 and average 34.29 ± 11.2 (n = 28). There is no obvious relationship between broods and maternal length. The length at birth arrives at total length 44cm. Based on the observation of egg diameter in the ovary of female blue shark, the maximum of egg diameter is 16-18 mm occurred in Nov. and at the same time fertilized eggs appear. Based on th e clasper length analysis, the smallest male matures at total length 174 cm (precaudal length 131 cm).