Aimed to access the genetic effect on growth traits and flesh components in juvenile grass carp(Ctenopharyngodon idella).Total of 288 juvenile grass carp at four months of age were random collected from artificial breeding program,and 273 of them were unambiguously assigned to sixteen full-sib families(from eight dams and nine sires) using twelve microsatellites.The contributions to the offspring by different families(full-sib and half-sib families) were showed with significant non-uniform distribution(P<0.01).Three growth traits(body weight,standard length,and condition factor) and two flesh components(protein and fat contents) of fish were detected in our study.The significant differences of three growth traits and protein content were detected among full-sib families and dam half-sib families(P<0.05),whereas,no significant differences of five traits were detected among sire half-sib families(P>0.05).The genetic parameters for these traits of juvenile grass carp were estimated using restricted maximum likelihood(REML) algorithm based on animal model.The heritability estimates for growth traits were 0.34 for body weight,0.33 for standard length,and 0.17 for condition factor,which were all significantly different from zero(P<0.05).Whereas,the heritability estimates for flesh components were 0.17 for protein content,and 0.20 for fat content,but not significantly from zero(P>0.05).Highly positive genetic correlation was found between standard length and body weight(0.82, P<0.01).Meanwhile,significantly positive genetic correlations were showed between condition factor to other traits studied except standard length(0.17-0.29, P<0.05).Therefore,selection for increased standard length of C.idella is expected to produce favorable improvement in body weight,but it may lead to unfavorable changes in condition factor and fat content.This should be taken into account in practical breeding programs of C.idella.