Interferon regulatory factors (IRFs) exhibit antiviral and antibacterial properties. In this study, we cloned the IRF8 genes of red sea bream (Pagrus major) and analyzed their expression following red sea bream iridovirus (RSIV) infection. Multi-sequence analysis revealed conserved features, such as the IRF-association domain, nuclear localization signal, and DNA-binding domain. Phylogenetic analysis demonstrated that PmIRF8 clustered with IRF8 from other fish species. Quantitative real-time PCR was employed to examine IRF8 expression in normal tissues, revealing high expression levels in the gill (26.7-fold), spleen (25.7-fold) and brain (22.6-fold). This finding aligns with previous research, which has established that IRF8 is associated with immune cell development and is highly expressed in lymphomyeloid tissues. Additionally, temporal expression of PmIRF8 following RSIV infection demonstrated an initial low expression in the gills, followed by an upregulation at 36 hours post-infection (hpi). A similar expression pattern was observed in the spleen. The liver showed variable expression, while the kidney exhibited an increase at 6 hpi, followed by another upregulation at 3 days post-infection. These results suggest that PmIRF8 plays a role in regulation and suppression during the immune response. These findings are corroborated by previous studies on other fish species. Overall, this investigation presents the characterization of IRF genes in red sea bream and provides foundational data for comparative analysis of IRF genes.