Herpes simplex virus type 1 ICP27 is a multifunctional protein responsible for viral replication, late gene expression, and reactivation from latency. ICP27 interacts with various cellular proteins, including Daxx. However, the role of interaction between ICP27 and Daxx is largely unknown. Since Daxx is known to repress NF-κB activity, there is a possibility that ICP27 may influence the inhibitory effect of Daxx on NF-κB activity. In this study, we tested whether ICP27 affects the NF-κB activity through its interaction with Daxx. Interestingly, ICP27 enhanced the Daxx-mediated repression of NF-κB activity. In addition, we found that sumoylation of Daxx regulates its interaction with p65. ICP27 binds to Daxx, inhibits Daxx sumoylation, and enhances p65 deacetylation induced by Daxx. Consequently, ICP27 represses the NF-B activity, by elevating the inhibitory effect of Daxx on NF-κB activity through desumoylation of Daxx. [BMB Reports 2017; 50(5): 275-280].