In order to investigate the relationship between estrogen receptor (ER) genes and growth of different sexes and ploidy in fish,loach（Misgurnus anguillicaudatus）whose female growth is faster than that of male and whose tetraploid growth is faster than diploid were selected as the research object in this study.We firstly cloned the cDNA sequences of three ER genes of loach,including ERα (1 821 bp),ERβ1 (1 008 bp) and ERβ2 (1 197 bp).Amino acid sequence alignment revealed that the loach ER genes shared higher similarity with corresponding subtypes of carps.Quantitative RT-PCR was used to detect the expression of ER genes at five growth stages of diploid loach,as well as in different tissues in diploid and tetraploid adults.The results showed that the three ER genes were differentially expressed in the brain,muscle,liver,and gonadal tissues of the male and female individuals before and after sexual maturity.Among them,the expression of ERα in the brain,muscle and gonad tissues of males was significantly higher than that of females (P<0.05),and expression in the female liver was generally higher than that in males (P<0.05).The expression levels of ERβ1 and ERβ2 in the testis were always high.Comparison results between different ploidy showed that expression of the three ER genes in the diploid brain were significantly higher than that of the tetraploids,and the expression levels of males were higher than that of females,with the expression of ERα being the most significant.The results of this study indicated that regardless of the difference between ploidy and sex growth, ERα appears to have relatively high expression in the brain of slow-growing (diploid,male) individuals.Therefore,we speculate that the ERα gene in the brain might have a certain inhibitory effect on the growth rate of fish.