Time of sex differentiation,as well as effects of 4-nonylphenol(NP)on growth and sex differentiation in juvenile Macrobrachium rosenbergii were studied by morphologic observation and histological sections.Ten zoea were collected randomly every 3 days,fixed in Bouin’s solution,then embedded in paraffin and sectioned.Transverse sections were stained with hematoxylin and eosin to identify its sex differentiation time.Juvenile M.rosenbergii were divided into 5 groups(n=200 per group):control,5,15,45,and 135 μg/L NP,respectively.All these juvenile M.rosenbergii were immersed in different doses of NP solutions for 30 days,and 50% NP solutions were renewed every 2 days to keep NP’s steady concentration.Ten juvenile M.rosenbergii were collected randomly from each group on 15,20,25,and 30 d,and both the body mass and length were measured respectively for the assessment of NP on growth.Thirty juvenile M.rosenbergii were collected randomly from each group on 30 d to identify their sex by outward features(gonopore,appendix masculine,etc)under anatomical lens,and 10 were fixed,embedded and sectioned to observe its gonad histology.Data were subjected to oneway analysis of variance followed by Duncan’s multiple rang test.Results showed that primordial germ cells(PGCs)appeared in 15 d larva; however,genital duct,a wrinkled and pimply plastron,and a sunken basal part on the 4^{th-5th walking legs appeared in 24 d larva in some M.rosenbergii.In addition,a rudiment of the appendix masculine on the internal of the 2nd-pleopod was found in 45 d larva in some M.rosenbergii,and gonads could be identified easily as testis and ovary,respectively. M.rosenbergii larvae were not affected in their body weight and length if treated by NP less than 15 d,however,they were inhibited significantly in a dosedependent manner if treated more than 20 d(P<0.05).Spermatogonium and oogonium were observed respectively in the testis and ovary in the control group on 30 d,however,gonads unidentified as male and female were found in the NPtreated groups,and the quantity of sex-unidentified M.rosenbergii increased with the doses of NP.Results suggested that the time of sex differentiation of larval M.rosenbergii occurred between 21 to 45 d larva and the change of external forms occurred before that of the internal forms.Furthermore,growth and testis development were inhibited possibly because of NP interfering with the processes of molt and vitellogenin synthesis.}