Avian influenza virus (AIV) is a significant zoonotic pathogen that causes infectious disease in various species and poses a serious threat to both the poultry industry and public health. Mammalian protein inhibitors of activated STAT2 (PIAS2) have been shown to affect viral replication by interacting with viral proteins. However, the role of chicken PIAS2 (chPIAS2) in regulating H6N2 subtype AIV replication remains unclear. In this study, we cloned chPIAS2 from primary chicken embryo fibroblast cells and identified that it contains five conserved domains. Overexpression of chPIAS2 promoted the replication of H6N2 AIV, although chPIAS2 expression was also induced during viral infection. We further found that chPIAS2 interacted with the H6N2 AIV nucleoprotein (NP) (DK65-NP) in the nucleus. ChPIAS2 promoted the SUMOylation of DK65-NP through its SUMO E3 ligase activity. We also confirmed that the lysine residues at positions 7, 48, 77, and 113 are the small ubiquitin-like modifier (SUMO) conjugation (SUMOylation) sites of DK65-NP. Collectively, our results indicate that chPIAS2 promotes H6N2 AIV replication by enhancing the SUMOylation of viral NP. In conclusion, our study reveals the role of chPIAS2 in AIV replication and provides new insights into the molecular mechanisms underlying AIV pathogenicity in poultry, suggesting a potential therapeutic target for avian influenza.