P31 gene of infect ious spleen and kidney necrosis virus ( ISKNV ) of Siniperca chuatsi had been sequenced. The open reading frame of the gene is 675 nucleotides long, encoding a putative protein of 225 amino acids with 25. 3kD. The 5. noncoding region has a TATA box and CAAT motif. A stem loop, a direct repeat sequence and a short dyad are contained downstream of the translation stop codon. The results of comparison of the homology with other iridoviruses p31 genes showed that ISKNV p31 gene has lower identities with others. Alignment of amino acid sequences and a phylogenetic tree of p31 genes of four iridoviruses have been constructed. The results indicated that ISKNV is different from the viruses of the genus Ranavirus and Lymphocystivirus.