Abstract: We investigated the biological characteristics of Katsuwonus pelamis which were collected by light-falling net fishery in the Nansha Islands sea area in May 2014 and April 2016. The results show that the dominant fork length ranged from 260 mm to 280 mm, accounting for 14.68% of the total samples. The dominant body weight ranged from 27 g to 100 g, accounting for 18.35% of the total samples. The somatic growing parameters (b value) between fork length and body weight was 3.403 9. The sex ratio of female to male was 1 : 0.9, and the sexual maturity was higher at Stage Ⅰ (47.71%) and Ⅳ (27.06%), and the proportion of males increased with increasing fork length. Gonad length was positively correlated with fork length significantly (P < 0.01). The fork length of the first gonadal maturity was 392.70 mm. Stage 1 and Stage 2 had the highest feeding intensities, accounting for 36.24% and 29.36% of the total samples, respectively. A descending trend was found from Stage 1 to Stage 4. The plumpness index ranged from 0.74 to 7.45 (averagely 2.53).