Vibrio harveyiis a causative agent of vibriosis that infects large yellow croaker（ Pseudosciaena crocea） as well as some other marine fish and brings severe loss to their culture. The development of vaccines against vibrio is recognized as a priority to the complement of existing control measures. Recent studies emphasized the role of the outer membrane protein （OMP） of pathogenic bacteria in protective anfigenicity. A target of protective immunity, OmpK, is the receptor for KVP40 which is a broad-host-range vibriophage. To investigate the possibility of OmpK as vaccine candidate, primes were designed according to OmpK gene sequence published in GenBank, and a piece of DNA sequence about 800 bp was amplified by PCR from genomic DNA of V. harveyi isolated fi＇om infected P. crocea. The gene was cloned into pGEM-Teasy vector and sequenced. The Blast alignment result indicated that it was indeed the outer membrane protein（OmpK） gene of V.hameyi. After its signal papfide sequence was discarded by PCR and the remains was inserted into E. coli expression vector pGEX-4T-2, a fusion expression vector pGEX-4T-OmpK was constructed, which can amply the expression of a 53 kD fusion protein GST-OmpK in E. coli BL21 when induced by IPFG. The fusion protein was purified and used as antigen to immunize the New Zealand rabbit, the antiserum with high antibody value was acquired. The Western-blotting shows that the anti-recombinant OmpK serum can specifically react to the 27 kD comtponent of natural Omps extracted fi＇om V. harveyi. This result indicates that the OmpK may be one of the important protective antigens of V. harveyi, and may play a role in protecting fish from infection of V. harveyi.