Anguilla japonica is one of the most important commercial catadromous species in Asia.Yangtze River Estuary serves as the major production area of larval eels and the only fishery waters of adult eels in China.In this study,we analyzed biological information for 153 migrating silver eels collected at Jingjiang reach of Jiangsu Province(32?01′27″N,120?25′56″E)from Oct.to Nov. in 2007 and 2008.Based on the analysis of the morphological index system of Japanese eels with Principal Components and R-cluster Analysis the reults indicated that A. japonica could be classified by “body size and head feature”,"detail characteristics about the anterior part of snout” and “eye diameter and pectoral fin size”.On the basis of this analysis,17 characteristics were normalized and further used for stepwise discriminant.And then 5 characteristics were picked out:fatness,vertical eye diameter/head length,body depth/body length,horizontal eye diameter/head length,snout shape.Thus the discriminant equations were built for classifying 75 samples and the accuracy rate was 89.3%.Furthermore,the other Japanese silver eels were also classified by this model and the success rate was 88.5%.ANOVA analysis showed that,apart from snout shape,the other four standardized characteristics between male and female populations were significantly different(P<0.001).Therefore,we concluded that the female silver eels collected from Yangtze River estuary were superior to males in the respect of fatness and body depth but smaller in eye diameter.