Abstract: The single-chain variable fragment of alpha fetoprotein (scFv-AFP) gene was sub-cloned into vector pET32a and transformed into E.coli BL21（DE3）host.The expression of scFv-AFP was improved by optimizing the expressing conditions by changing different inducing temperature,time and concentration of IPTG.Then the inclusion body was denatured and renatured,the refolding yield of protein from inclusion body is about 37.38%.The competitive ELISA method was used to determine the immunologic activity of renatured protein,and the inhibition rate reached 54.13% while the concentration ratio of scFv and parent monoclonal antibodies was 16 ∶1.This work would be helpful for the further application and modification of scFv-AFP.