During viral infection, RIG-I-like receptors (RLRs) are cytoplasmic pattern recognition receptors that recognize and bind to viral RNA components, initiating the transcription of interferon-related genes, inflammatory cytokines and other factors, thereby triggering the cellular production of an antiviral innate immune response. The protein inhibitor of activated signal transducer and activator of transcription (STAT) (PIAS) protein family has become a hot research topic due to its extensive involvement in the regulation of cytokines, inflammatory factors and innate immune signaling pathways. In the present study, we investigated the role of fish PIASy in Singapore grouper iridovirus (SGIV) and red spotted grouper nervous necrosis virus (RGNNV) infections. The homologous sequence of orange-spotted grouper (Epinephelus coioides) PIASy gene (EcPIASy) was cloned and characterized, which encoded a 498-amino acid protein with 99.20 % homology to Plectropomus leopardus. EcPIASy is expressed mainly in gills, blood, and liver. Subcellular localization showed that EcPIASy was uniformly distributed in the nucleus. Overexpression of EcPIASy promoted SGIV and RGNNV replication, and inhibited the expression of interferon related genes and pro-inflammatory factors induced by viruses. In addition, EcPIASy interacts with RLR signaling pathway-related genes EcMDA5, EcIRF3 and EcIRF7, whereas the interaction between EcPIASy and EcIRF3 does not depend on any specific structural domain of EcPIASy. The results provide a better understanding of the relationship between PIASy and viral infection in fish.