The human herpesvirus-6 (HHV-6) infection induces cell-cycle arrest. In this study, we found that the HHV-6-encoded U14 protein induced cell-cycle arrest at G2/M phase via an association with the cellular protein EDD, a mediator of DNA-damage signal transduction. In the early phase of HHV-6 infection, U14 colocalized with EDD dots in the nucleus, and similar colocalization was also observed in cells transfected with a U14 expression vector. When the carboxyl-terminal region of U14 was deleted, no association of U14 and EDD was observed, and the percentage of cells in G2/M decreased relative to that in cells expressing wild-type U14, indicating that the C-terminal region of U14 and the U14-EDD association are critical for the cell-cycle arrest induced by U14. These results indicate that U14 is a G2/M checkpoint regulator encoded by HHV-6.