Grass carp reovirus (GCRV) has a genome consisting of 11 double-stranded RNA,and possesses several structural proteins.The VP5 protein is one of the structural proteins in the core capsid encoded by the M5 gene of GCRV-GD108,a reovirus strain which was isolated from grass carp cultured in Guangdong and had been identified by our lab recently.Primers with restriction enzyme digesting sites were designed based on the cDNA of M5 gene.The amplification products of M5 gene were digested and cloned into prokaryotic expression vectors.Two recombinant protein expression vectors,pET30c-M5 and pColdⅡ-M5,which had been identified by PCR,enzyme digestion and sequence analysis,were transformed into E.coli strains,respectively.Then the recombinant expression strains were induced.The effects of culture medium,induction time,temperature and IPTG levels were analyzed,and suitable conditions for the expression of the target protein were proposed.The results of SDS-PAGE and Western blot showed that the target protein VP5 with molecular weight around 80 ku was obtained,but the recombinant protein was mainly presented in inclusion bodies.The inclusion bodies were then denatured,dialyzed and renatured to get the recombinant protein.The target protein,which was expressed by pET30c-M5/BL21(DE3) accounted for 22.5% of the total bacteria proteins,and was highly purified (>95.0%).The pET30c-M5 is considered to be an engineering strain suitable for large scale expression for it cost less time of inducing and got higher production than pColdⅡ-M5.