The nodaviridae , which include two genera : alphanodavirus and betanodavirus , are a family of small , isometric and non2enveloped RNA viruses. Alphanodaviruses primarily infect insects and betanodaviruses infect fish. Their genomes , which are among the smallest known for animal viruses , consist of two co2encapsidated positive2sense RNA segments : RNA1 encodes the RNA2dependent RNA polymerase (RdRp) which replicates the viral genomes , while RNA2 encodes a precursor to the coat protein. Based on the coat protein sequence , betanodaviruses are categorized into four different genotypes : TPNNV (tiger puffer nervous necrosis virus ) , SJNNV (stripedjack nervous necrosis virus ),BFNNV (barfinflounder nervous necrosis virus ),RGNNV (red2 spotted grouper nervous necrosis virus ) . Orange2spotted grouper ( Epinephelus coioides) nervous necrosis virus (OGNNV) is the causative agent of viral nervous necrosis (VNN) in larval and juvenal orange2spotted grouper fish. In this study , total RNA was extracted from the head of orange2spotted grouper infected with VNN. A pair of primers were designed according to the homogenus gene sequences , which have been submitted to GeneBank , from other fish nervous necrosis virus (NNV) . The forward (sense) primer contained Sac Ⅰsite and the reverse (antisense) primer contained Hind Ⅲsites. One target fragment was amplified by means of reverse2transcriptase polymerase chain reaction (RT2PCR) . After digestion with Sac Ⅰ and Hand Ⅲ, the RT2PCR products were ligated into the pET32 plasmid vector and transformed into E. coli BL21. The RT2PCR product and recombinant plasmid were sequenced , respectively. The coat protein gene of OGNNV was 1017 bases , encoded a protein of 338 amino acid with molecular mass of 37059. 88 da , and with isoelectric point (IP) of 8. 87. The sequence of the coat protein gene from OGNNV was submitted to GeneBank and the accession number was AF534998. The nucleotide sequence of the coat protein gene from OGNNV was aligned with four betanodaviruses : SJNNV , TPNNV,RGNNV,BFNNV and one alphanodavirus: BBV (Black beetle virus ). Analyses indicated that the nucleotide length of the coat protein gene from OGNNV was six bases shorter than SJNNV and TPNNV , and that the length of encoded protein was 2 aa shorter than SJNNV and TPNNV , and that the length of nucleotide sequence and encoded protein was the same as RGNNV and BFNNV. The sequence similarities between the coat at nucleotide proteingenefromOGNNVandfourfishnodaviruses of 22 % with (SJNNV,TPNNV,RGNNV,BFNNV) was 76 % ,76 % , 81.4% and 99 %, respectively. The coat protein gene from OGNNV had the highest identity of 99 % with RGNNV at nucleotide level , and had low identity BBV level . Phylogenetic comparisons of OGNNV were performed against five nodaviruses. Analyses showed that the coat protein sequence related to BBV. Neutralization epitope analysis revealed that OGNNV completely preserved in RGNNV genotype , at aa 254 -256 with RGNNV. of OGNNV was closely related to four fish nodaviruses , and was most closely related to RGNNV , but was not shared the same PDG, which was These results suggested that OGNNV belonged to RGNNV genotype , but was different from insect nodaviruses.