To study the function of the estrogen receptor α (ERα) gene,the recombinant pMAL- ERα was constructed and expressed in TB1 E.coli.Partial cDNA encoding ERα was amplified from total RNA of swamp eel (Monopterus albus) ovary by reverse transcription-polymerase chain reaction (RT-PCR).The analysis of the sequence data indicated that the cDNA fragment was 945 bp in length,encoding 315 amino acid residues.The amplified cDNA fragment was cloned into the prokaryotic expression vector,pMAL-c2x and the recombinant plasmid was then transformed into E.coli TB1.ERα-MBP fusion protein was obtained after the IPTG addition into the growth media.SDS-PAGE analysis showed that the ERα-MBP was expressed after induction by IPTG for 4 h.A protein band of 78.1 ku appeared on SDS-PAGE gel and was identified by Western blot.The production of the recombinant protein was about 42.3% of total bacteria protein.After purification and cleavage of the fusion protein,purified ERα protein was obtained.Then the purified protein was used to immunize ICR mice to produce anti- ERα antibody.This purified protein could significantly elicit specific antibody response in immunized mice compared with the control groups,and the titers against ERα reached the peak (1.158±0.232) at the 7th week.The immunohistochemical analysis showed that the polyclonal antibody can induce specific reaction with ERα receptor in ovary and produced brown precipitation on the ovary cell membrane.