Herpes simplex virus type 1 ICP27 is a multifunctional protein which is responsible for viral replication, late gene expression, and reactivation from latency. It has been reported that ICP27 interacts with various cellular proteins including Daxx. However, the role of interaction between ICP27 and Daxx is largely unknown. Since Daxx has been reported to repress NF-B activity, there is a possibility that ICP27 may influence the inhibitory effect of Daxx on NF-B activity. In this study, we tested whether ICP27 affects NF-B activity through its interaction with Daxx. Interestingly, ICP27 enhanced Daxx-mediated repression of NF-B activity. In addition, we found that sumoylation of Daxx regulates its interaction with p65. It turned out that ICP27 binds to Daxx, inhibits Daxx sumoylation, and enhances p65 deacetylation induced by Daxx. Therefore ICP27 represses NF-B activity by elevating the inhibitory effect of Daxx on NF-B activity through desumoylation of Daxx.