Abstract: We applied paraffin section method to investigate the reproductive features for female bigeye tuna (Thunnus obesus) in the southern Pacific Ocean (SPO), using ovarian tissues sampled at sea during 2010~2013. Maturity stage and fecundity were estimated under a microscope. The results show that the development of ovary was divided into five stages: 1 (immature), 2 (maturing ), 3 (maturing ) , 4 (ovulating) and 5 (ovulated). Female gonad somatic index (GSI) ranged from 0.26 to 8.58 (average 3.56), increasing with the increase of fork length. Length at 50% maturity was 116.32 cm. Average batch fecundity was 1.09106 pcs, and average relative fecundity was 20.5 pcsg-1. Cluster analysis shows that there were three classes in terms of similarity in catch depth, i.e., Stages 2 and 3, Stages 1 and 4, and Stage 5. It is suggested that bigeye tuna reached first sexual maturity at earlier ages in SPO than in other areas, probablydue tooverfishing.