Based on the biological data of bigeye tuna measured from the longlining ground of the Central Atlant ic Ocean from Jun. 2001 to Oct. 2001, this paper analyzed the bigeye tuna. s maturity stages of the gonad, feeding intensity, species compo sition of prey, sex ratio , fork length distribution, relationships between fork length and dressed weight, fork length and round weight, round weight and dressed weight by statistic and regression methods. The results indicate: ( 1) Maturity at .- . of the gonad are dominant with the highest percentage of . ( 30. 11% ) . ( 2)The feeding intensity is mainly in the class 1, class 2 or class 3, totally 83. 16% . ( 3) In the bigeye tuna. s species composition of prey, the percentage of miscellaneous f ish or cephalopod is relatively high, 38. 05% or 30. 48% respectively. Catch rate of bigeye tuna can be enhanced when cephalopod is used as the bait. ( 4) The male-female ratio is 2B1. This pattern might result f rom elevated mortality of adult females. ( 5) The fork length distribution is suitable for the normal. The dominant fork length is 1. 13- 1. 49m, 64. 16% , with the mean value of 1. 32m. ( 6) The relationship between fork length and dressed weight. ( 7) The relationship between fork length and round weight. If the fork length is the same, the round weight converted in this paper. s formula is a litt le lighter than the round weight converted in Parks. s formula concluded at 1981 of the longline bigeye tuna catch. It might be caused by the different sampling areas or sampling time. ( 8) The relationship between round weight and dressed weight . The round weight conversion factor in this paper is a little higher than the ICCAT. It might be caused by the different processing methods. ICCAT is recommended to adapt this paper. s conversion factor.