Yellowfin tuna (Thunnus albacares) is the main target species for Chinese tuna fisheries fleets in Indian Ocean. According to a total of 1233 yellowfin tuna samples collected by Chinese national observers in the central-western Indian Ocean during two stages (Oct. 2012-Jan. 2013 and Oct. 2013-Feb. 2014),we conducted the study on the reproductive biology of this tuna. The main reproductive biological parameters were estimated in this study. The results indicated: (1)The relationship between fork length and dressed weight for female and male were W=7×10^-6L^3.244 and W=6×10^-6L^3.197, respectively. (2) From these samples, the total sex ratio of female to male was 0.74:1, and the sex ratio was 0.69:1 in such mature samples. (3) The gonadsomatic index for female and male were calculated from 0.39 to 5.92, and from 0.44 to 3.37, respectively.(4) The logistic regression was described the relationships between fork length and maturity for both female and male which were P=1/[1+e^{0.08276×(122.991-FLm)}] and P=1/[1+e^{0.03767×(118.618-FLm)}], respectively. (5)The maturity analysis showed that the percentages of female and male samples which reached mature were highest in January and December, respectively. And the lowest percentages of both female and male were in February. (6) The cut-off point for larger and smaller groups was 115 cm,and the percentage of larger female and male were 63.13% and 75.40%,respectively, which was significantly different between male and female. This study will contribute to the evaluation for this fish resources.